Remove redundant g_SurfaceMutex. This mutex become redundant after recent CL: https://chromium.googlesource.com/angle/angle/+/23ad4fa2be35aed303cbb8c2d632a04714354ef0 Don't hold global surface lock during AcquireNextImage Every place in the code where `ANGLE_SCOPED_GLOBAL_SURFACE_LOCK()` is used also uses `ANGLE_SCOPED_GLOBAL_LOCK()`. Bug: angleproject:6851 Change-Id: I464b6ca74743c9ee9fa23caad216f0e26c480655 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4385293 Commit-Queue: Igor Nazarov <i.nazarov@samsung.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Charlie Lao <cclao@google.com>