chore: cleanup release-please config (#2264)

- Remove redundant options already declared at the top level.\n- Remove bumpMinorPreMajor for repositories after the first major release.

Co-authored-by: Blake Li <blakeli@google.com>

Author: diegomarquezp

.github/release-please.yml

@@ -2,12 +2,6 @@ bumpMinorPreMajor: true
 handleGHRelease: true
 releaseType: java-yoshi
 branches:
-  - bumpMinorPreMajor: true
-    handleGHRelease: true
-    releaseType: java-yoshi
-    branch: java7
-  - bumpMinorPreMajor: true
-    handleGHRelease: true
-    releaseType: java-yoshi
-    branch: protobuf-4.x-rc
-    manifest: true
+    - branch: java7
+    - branch: protobuf-4.x-rc
+      manifest: true