Add common PGO profiles for hwui/skia

Bug: http://b/120096099

These are from build 5339666 (2019-02-27).

Unlike during P, we're now merging profiles from both the 32-bit and
64-bit benchmarks.  This speeds up the 32-bit benchmarks better, and
slows down only hwuimacro by a tiny bit (0.2%).

Also remove the skia/ subdirectory.  Skia uses the same profdata as hwui
[1], since we're also using ThinLTO and ThinLTO expects that all object
files are compiled with the PGO profiles.  The hwui.profdata now
includes profiles from skia_nanobench as well.

Test: Validate PGO performance on skia_nanobench, hwuimacro, hwuimicro
on Crosshatch.  Performance numbers are in go/android-pgo-in-q

Change-Id: I63bf48ccf970e9d803524a5c7b98bad62213e571