Remove gradient SkFixed position records

At this point they are only used to build a cache key.  Replace with
float positions and delete the supporting code.

Change-Id: Ida12fd39ed3f612a807de4505c7398838e0693be
Reviewed-on: https://skia-review.googlesource.com/64940
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
2 files changed