Remove the existing_rule check
Remove the existing_rule check

This is needed for building with Bazel 0.2.3 until bazelbuild/bazel#1277 is fixed.

Fixes #10.

Change-Id: Ia7e8dfd5d899dd65f329d7bf7fd807128046ee86

bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration