Don't enforce Go version using //go:build in main.go files

These build tags lead to a rather unhelpful error message when compiling
an outdated Go versions, e.g.

    package github.com/cilium/cilium/daemon: build constraints exclude all Go files in ...

Nothing in the error messages indicates that this is due to an outdated
Go toolchain version and this has been a source of confusion several
times for several developers.

It's also brittle in a way that if a developer adds a new tool with a
main func and forgets adding the //go:build line it will not be enforced
by tooling. The update-go-version make target will only cover existing
//go:build go1.X lines.

We have other checks in place to guarantee that Cilium is built using
the correct Go version (namely the go directive in go.mod, the
check-go-version make target, the dev-doctor tool and various CI
checks), so drop these build tags.

Signed-off-by: Tobias Klauser <tobias@cilium.io>

Makefile

@@ -656,14 +656,6 @@ else
 	@$(ECHO_CHECK) "Installed Go version $(GO_INSTALLED_MAJOR_AND_MINOR_VERSION) matches required version $(GO_MAJOR_AND_MINOR_VERSION)"
 endif
 
-update-go-version: ## Update Go version for all the components (images, CI, dev-doctor etc.).
-	# Update Go version in main.go.
-	$(QUIET) for fl in $(shell find .  -name main.go -not -path "./vendor/*" -print); do \
-		sed -i \
-			-e 's|^//go:build go.*|//go:build go$(GO_MAJOR_AND_MINOR_VERSION)|g' \
-			$$fl ; \
-	done
-
 dev-doctor: ## Run Cilium dev-doctor to validate local development environment.
 	$(QUIET)$(GO) version 2>/dev/null || ( echo "go not found, see https://golang.org/doc/install" ; false )
 	$(QUIET)$(GO) run ./tools/dev-doctor

bugtool/main.go

@@ -1,10 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 // Copyright Authors of Cilium
 
-// Ensure build fails on versions of Go that are not supported by Cilium.
-// This build tag should be kept in sync with the version specified in go.mod.
-//go:build go1.20
-
 package main
 
 import (

cilium-health/main.go

@@ -1,10 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 // Copyright Authors of Cilium
 
-// Ensure build fails on versions of Go that are not supported by Cilium.
-// This build tag should be kept in sync with the version specified in go.mod.
-//go:build go1.20
-
 package main
 
 import "github.com/cilium/cilium/cilium-health/cmd"

cilium-health/responder/main.go

@@ -1,10 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 // Copyright Authors of Cilium
 
-// Ensure build fails on versions of Go that are not supported by Cilium.
-// This build tag should be kept in sync with the version specified in go.mod.
-//go:build go1.20
-
 package main
 
 import (

cilium/main.go

@@ -1,15 +1,9 @@
 // SPDX-License-Identifier: Apache-2.0
 // Copyright Authors of Cilium
 
-// Ensure build fails on versions of Go that are not supported by Cilium.
-// This build tag should be kept in sync with the version specified in go.mod.
-//go:build go1.20
-
 package main
 
-import (
-	"github.com/cilium/cilium/cilium/cmd"
-)
+import "github.com/cilium/cilium/cilium/cmd"
 
 func main() {
 	cmd.Execute()

clustermesh-apiserver/main.go

@@ -1,10 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 // Copyright Authors of Cilium
 
-// Ensure build fails on versions of Go that are not supported by Cilium.
-// This build tag should be kept in sync with the version specified in go.mod.
-//go:build go1.20
-
 package main
 
 import (

daemon/main.go

@@ -1,15 +1,9 @@
 // SPDX-License-Identifier: Apache-2.0
 // Copyright Authors of Cilium
 
-// Ensure build fails on versions of Go that are not supported by Cilium.
-// This build tag should be kept in sync with the version specified in go.mod.
-//go:build go1.20
-
 package main
 
-import (
-	"github.com/cilium/cilium/daemon/cmd"
-)
+import "github.com/cilium/cilium/daemon/cmd"
 
 func main() {
 	cmd.Execute()

hubble-relay/main.go

@@ -1,10 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 // Copyright Authors of Cilium
 
-// Ensure build fails on versions of Go that are not supported by Cilium.
-// This build tag should be kept in sync with the version specified in go.mod.
-//go:build go1.20
-
 package main
 
 import (

operator/main.go

@@ -1,10 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 // Copyright Authors of Cilium
 
-// Ensure build fails on versions of Go that are not supported by Cilium.
-// This build tag should be kept in sync with the version specified in go.mod.
-//go:build go1.20
-
 package main
 
 import "github.com/cilium/cilium/operator/cmd"

plugins/cilium-cni/main.go

@@ -1,10 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 // Copyright Authors of Cilium
 
-// Ensure build fails on versions of Go that are not supported by Cilium.
-// This build tag should be kept in sync with the version specified in go.mod.
-//go:build go1.20
-
 package main
 
 import (

plugins/cilium-docker/main.go

@@ -1,10 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 // Copyright Authors of Cilium
 
-// Ensure build fails on versions of Go that are not supported by Cilium.
-// This build tag should be kept in sync with the version specified in go.mod.
-//go:build go1.20
-
 package main
 
 import (