rm java/examples/pingpong and many of its 3rdparty deps

rm {src|tests}/java/com/pants/examples/pingpong

rm -r 3rdparty/jvm/com/

3rdparty/BUILD -= ['guice', 'easymock']

3rdparty/BUILD -= ['mockito'] <- pingpong didn't use this; 'git grep' says nothing else did either

Testing Done:
https://travis-ci.org/pantsbuild/pants/builds/28428093

Reviewed at https://rbcommons.com/s/twitter/r/596/