They were removed in 137c74d1 since it was believed they were unnecessary.
However, since they are in a macro and not a rule, they are relative to the
caller, not their definition.
Added building the examples to the kokoro CI. Note that this means the examples
are built twice: once in grpc-java's build and once in their own (because it
has a WORKSPACE). Given that the Bazel build is our fastest build, this
slowdown won't probably be an issue.