SF: Cleanup EventThread Part 2

De-refbase EventThread and a bunch of related classes. Convert from
usign StrongPointer to std::unique_ptr to hold owned references, or bare
pointers for unowned references.

I did not see any need for using std::shared_ptr, or anything else, as
SurfaceFlinger appeared to own all the objects, and they were created
once and not really destroyed afterwards.

Test: Things seem to still work on a Pixel XL
Bug: None

Change-Id: Ifff32118d31bc1bb51e38df695ebe5cf86d2bb6d