revert #801 after bazel toolchains correctly deal with target dependencies

See thread:

https://groups.google.com/forum/#!msg/bazel-discuss/vXrG6uFL5V8/RjK8_chaEgAJ

and the change we had to do on #801 to deal with it.

cc @katre @ianoc

Start by reading issue #801 and the linked bazel-discuss thread to understand the target-dependency problem and the change made in response. Identify the files changed by #801, then determine whether those changes can be reverted now that Bazel toolchains correctly handle target dependencies. Done means the unnecessary workaround from #801 is reverted without breaking the Scala rules.

Written by the indexing model from the issue text.