Remove unused files in third_party/libsdl.

Change-Id: I44c95341e7bc631322a9802bce3fdc5a0e8c4bb5
Reviewed-on: https://skia-review.googlesource.com/8066
Commit-Queue: Mike Klein <mtklein@chromium.org>
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Hal Canary <halcanary@google.com>
11 files changed