Run Starlark tests only with Python 3
Run Starlark tests only with Python 3

The macro `py2and3_strict_test` was generating twice as many tests, but we don't need them.

RELNOTES: None.
PiperOrigin-RevId: 318835824

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