Remove deprecated magnifier filter header

Bug: skia:11230
Change-Id: I54f3ca4b0a8e492c18986f760f2a2b077a05e68a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/371960
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
6 files changed