Remove unused param to SkGIFFrameContext ctor

After updating the transparency index code, the reader parameter to
SkGIFFrameContext's ctor is no longer needed. This patch removes it.

BUG=skia:7069

Change-Id: If129f825639e8d43d73794adca2de09785f56a3c
Reviewed-on: https://skia-review.googlesource.com/52602
Commit-Queue: Chris Blume <cblume@chromium.org>
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
2 files changed