SF: Remove EventControlThread

EventControlThread was a HWC workaround dating back to K for toggling
VSYNC off the main thread, but as of R it defers back to main only to
incur context switches.

Clean up TestableScheduler construction to skip creating DispSync and
timer threads, which fixes several gMock warnings of unexpected calls.

Remove virtual destructors for non-polymorphic interfaces.

Bug: 160012986
Test: systrace
Test: libsurfaceflinger_unittest
Change-Id: I01360016a7dba79dc905f250753e6fce34af0a90