Remove IncompleteShortIntPrecision workaround flag.

This was added at http://review.skia.org/109003 because the CCPR
shaders used `short` and expected full 16-bit int precision from
a `short` type. Full 16-bit ints were _not_ promised by the ES2
spec, so if the shader was not compiled with `#version 300` at
the top, this was probably just an error in our code that didn't
need a workaround bit at all. However, this all happened in 2018
and it's too late to test that theory without setting up a new
test case from scratch.

At present, no code in Skia relies on short ints as far as I can
see, and Runtime Effects never promised `short` precision above
the baseline ES2 guarantees, so this workaround is unused.

Change-Id: Iba8bbe00a7683be306b211a57a4a7eef4f6e3b9f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/758318
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
9 files changed