Clean up definition of r8_support to stop confusing Bazel.
Clean up definition of r8_support to stop confusing Bazel.

java_library targets with deps must have sources.

Closes #11266.

PiperOrigin-RevId: 309391125

davidzchen/bazel,ulfjack/bazel,ulfjack/bazel,davidzchen/bazel,katre/bazel,werkt/bazel,werkt/bazel,safarmer/bazel,akira-baruah/bazel,bazelbuild/bazel,ulfjack/bazel,twitter-forks/bazel,perezd/bazel,akira-baruah/bazel,werkt/bazel,cushon/bazel,werkt/bazel,meteorcloudy/bazel,akira-baruah/bazel,safarmer/bazel,ulfjack/bazel,twitter-forks/bazel,safarmer/bazel,bazelbuild/bazel,ulfjack/bazel,perezd/bazel,katre/bazel,twitter-forks/bazel,davidzchen/bazel,twitter-forks/bazel,cushon/bazel,cushon/bazel,twitter-forks/bazel,werkt/bazel,safarmer/bazel,bazelbuild/bazel,meteorcloudy/bazel,ButterflyNetwork/bazel,ButterflyNetwork/bazel,twitter-forks/bazel,perezd/bazel,perezd/bazel,cushon/bazel,ulfjack/bazel,davidzchen/bazel,werkt/bazel,katre/bazel,meteorcloudy/bazel,akira-baruah/bazel,bazelbuild/bazel,bazelbuild/bazel,davidzchen/bazel,safarmer/bazel,davidzchen/bazel,meteorcloudy/bazel,perezd/bazel,cushon/bazel,ButterflyNetwork/bazel,safarmer/bazel,meteorcloudy/bazel,bazelbuild/bazel,katre/bazel,katre/bazel,twitter-forks/bazel,meteorcloudy/bazel,katre/bazel,cushon/bazel,akira-baruah/bazel,ulfjack/bazel,perezd/bazel,davidzchen/bazel,perezd/bazel,meteorcloudy/bazel,ButterflyNetwork/bazel,ButterflyNetwork/bazel,akira-baruah/bazel,ButterflyNetwork/bazel