[ThreadStateCoordinator] Remove Event classes

Summary:
This is a cleanup patch for thread state coordinator. After making processing of all events
synchronous, there is no need to have a a separate class for each event. I have moved back
processing of all events back into the TSC class. No functional change.

Test Plan: All tests continue to pass.

Reviewers: chaoren, vharron

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D9254

llvm-svn: 236576