Move libadbd_auth, libadbd_fs to adbd_system_binaries.

The required block inside the definition of "adbd" does nothing: we get
the libraries it contains via direct dependency when building from
source, and not at all when using a prebuilt. Move them to a phony
rule that's explicitly listed in PRODUCT_PACKAGES.

Bug: http://b/157709367
Test: treehugger
Change-Id: I97c0889558482cfbe18ae91b39b6889d3fee877c
(cherry picked from commit e572f2fc44be87f48a605c7c603401b712cbf841)

Former-commit-id: 0217d52d0157b0d66e778df58ad99f50abb78366

adb/Android.bp

@@ -605,25 +605,25 @@ cc_binary {
             ],
         }
     },
-
-    required: [
-        "libadbd_auth",
-        "libadbd_fs",
-    ],
 }
 
 phony {
-    name: "adbd_system_binaries",
+    // Interface between adbd in a module and the system.
+    name: "adbd_system_api",
     required: [
+        "libadbd_auth",
+        "libadbd_fs",
         "abb",
         "reboot",
         "set-verity-state",
     ]
 }
 
 phony {
-    name: "adbd_system_binaries_recovery",
+    name: "adbd_system_api_recovery",
     required: [
+        "libadbd_auth",
+        "libadbd_fs",
         "reboot.recovery",
     ],
 }