Remove deprecated merge image filter header

Bug: skia:11230
Change-Id: I50a9fb86a9054b96b3088b06f625dea418f53db8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/371962
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
6 files changed