[NativeProcessLinux] fold ThreadStateCoordinator into NPL

Summary:
Since all TSC operations are now executed synchronously, TSC has become a little more than a
messenger between different parts of NativeProcessLinux. Therefore, the reason for its existance
has disappeared.

This commit moves the contents of the TSC into the NPL class. This will enable us to remove all
the boilerplate code in NPL (as it stands now, this is most of the class), which I plan to do in
subsequent commits.

Unfortunately, this also means we will lose the unit tests for the TSC. However, since the size
of the TSC has diminished, the unit tests were not testing much at this point anyway, so it's not
a big loss.

No functional change.

Test Plan: All tests continue to pass.

Reviewers: vharron, chaoren

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D9296

llvm-svn: 236587