Remove thrift/test/UnionTest_cpp (duplicate of UnionTest_cpp2, but for cpp1)
Remove thrift/test/UnionTest_cpp (duplicate of UnionTest_cpp2, but for cpp1)

Summary: Currently Thrift tests are the last places that use cpp1 and compatibility mode, so I'm switching them to cpp2 and removing duplicates.

Reviewed By: yfeldblum, stevegury

Differential Revision: D7224677

fbshipit-source-id: 2582414569ca102c190103cd58b8698c3228f23c

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift