Remove SkLiteDL::makeThreadsafe().

It's not used, and removing it cuts a branch in DrawDrawable::draw().

Change-Id: I15d13dda1ec594c525f5d108e208b00286c2d09f
Reviewed-on: https://skia-review.googlesource.com/9174
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
3 files changed