Remove SkTSearch and SkFixed uses from SkiaInterpolator

This inlined (and simplified) SkTSearch from Skia [1], as well
as removing SkAsserts.

All of these are considered private to Skia.

This should be tested in CTS via android.graphics.Interpolator, e.g.
    Test: atest CtsGraphicsTestCases

[1] https://github.com/google/skia/blob/372a0857bf47009a6b245679a5d926b3bf5ca92a/src/base/SkTSearch.h#L41

Change-Id: Ifcc410adc768480fdc998919ba9e7aeed52336b7
Bug: skbug.com/13983