[sdk-platform-java] investigate if test golden files are orphaned

context: https://github.com/googleapis/sdk-platform-java/pull/3550
At start of 2025, https://github.com/googleapis/sdk-platform-java/issues/3547 causes test failures on license header year difference. These tests are missed in the original fix, and did not cause any ci test failures without the fix.
Suspecting that these tests are not actually used in test assert, or might be orphaned golden files that used to be used, and did not remove.
Investigate and remove these golden files if not used.