Remove legacy code from annotation build.gradle
Remove legacy code from annotation build.gradle

- We always build with java8 now.
- We set preserveFileTimestamps and reproducibleFileOrder in
  AndroidXPlugin.
- Remove javadoc jar from annotations, we have since stopped publishing
  them as they are not surfaced anywhere. Developers get source jars in
  studio instead.

Test: ./gradlew annotation:jar
Change-Id: I65c15dcec4e52eff5f6959b0d54eec35ecc56880

androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx