There is no good reason why depending on //lib/truth should free
downstream libraries from needing a direct dep on //lib/guava or
//lib/junit. Exporting the deps was probably just oversight, since the
distinction between exports and runtime_deps in WORKSPACE is not
obvious, and there are probably other bad examples.
Change-Id: I1530106d642167eaa25222cc95c3996478728e15
1f0e48a727