Delete the legacy linear gradient impl

Dead code at this point.

Change-Id: I0eb705195446ec084ead49c9f712bf19d8892305
Reviewed-on: https://skia-review.googlesource.com/48020
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed