Remove SK_SCALAR_IS_FLOAT checks, they are always true

SkScalar used to be float or double (or fixed) but has been float
only since 2017
https://github.com/google/skia/commit/529bcd6db7ebfa3a9e4898696cfc869839045176

Change-Id: I822ad61e6522e7c0757905b7d0d1b4da920c418f