SK_USE_SDL is never defined

This CL also removes dead code, SkOSWindow_SDL.cpp.

Change-Id: I659dc271a4bcceba7fe29ac5ac6e79d684153870
Reviewed-on: https://skia-review.googlesource.com/8070
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Hal Canary <halcanary@google.com>
3 files changed