ORC-1560: Remove Java11 and clang variants from docker/os-list.txt …

…in `branch-1.8`

### What changes were proposed in this pull request?

This PR aims to remove Java11 and clang variants from `docker/os-list.txt` in `branch-1.8`.

### Why are the changes needed?

After the following PR, `GitHub Action CI` runs all supported OSes and variants (Java 11/clang) at every commit.
- #1699

### How was this patch tested?

Manual review because this is a removal.

Closes #1703 from dongjoon-hyun/ORC-1560.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

docker/os-list.txt

@@ -5,6 +5,3 @@ ubuntu18
 ubuntu20
 ubuntu22
 fedora37
-debian10_jdk=11
-ubuntu20_jdk=11
-ubuntu20_jdk=11_cc=clang