Remove the last vestiges of THRIFT_OVERLOAD_IF from THRIFT-1316

In THRIFT-1316 some macros were added that have proven to be unnecessary. They were partially eliminated in THRIFT-3083, and this traces the removal of what was left. In addition, TOutput was moved to its own class, and since TThrift.cpp only contained TOutput code, it was renamed.

Boost gained this mechanism internally in a release after boost-1.33 which is what was required when THRIFT-1316 was added to the codebase. With the current minimum requirement of 1.53, it is safe to remove THRIFT_OVERLOAD_IF. Tests confirm this (in TServerIntegrationTest).