Remove SDL from DEPS (and SDL example that used it)

Change-Id: Ia18badfdd174015b67ce09ae3ec3180df0481710
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/413378
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
6 files changed