Unbreak fboss-oss; remove old cpp1 thrift switch_config code
Unbreak fboss-oss; remove old cpp1 thrift switch_config code

Summary:
Boris's change to switch_config.thrift is completely legal with
the cpp2 driver, but for historical reasons, open source FBOSS
built with cpp1 and cpp2, which broke the build.  Removing
the cpp1 builds seems to fix the problem.

Reviewed By: boryas

Differential Revision: D5626845

fbshipit-source-id: cfb98fbb68e1b350d5947653179406d762ab3642

peterlei/fboss,peterlei/fboss,peterlei/fboss,peterlei/fboss