SF: Fix an EventThread deadlock

EventThread::removeDisplayEventConnection tried to acquire the mutex,
however the caller (eventThread::threadMain()) already had it.

The fix was to not acquire the mutex, since threadMain() was the only
caller.

Bug: 73256320
Test: Can toggle "Show taps" from dev options without lockup.
Change-Id: I855b19b3d0ac9e0ea05604cc7b077f4a5030a00b