Remove GrTextureStripAtlas, textured gradients use independent textures

The texture strip atlas code path has been disabled without performance
regressions since 8/3/18, so this deletes it completely from the code
base since it is complex and difficult to manage.

GrTextureStripAtlas, GrDynamicTextureStripAtlas, and
GrDDLTextureStripAtlas completely deleted, everything else is cleaning
up references/dead code using the atlas.

Bug: skia:
Change-Id: Ieb967b6e291a1d76da62fce9fa384acbda8c51c0
Reviewed-on: https://skia-review.googlesource.com/150472
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
13 files changed