Remove D3D #includes from GrBackendSemaphore

This also removes the fIsInitialized which is no longer
necessary to keep the state consistent.

Change-Id: I808c4dd2adca03496a069305c27bcd0ccfde732c
Bug: b/293490566
Cq-Include-Trybots: luci.skia.skia.primary:Test-Win11-MSVC-Golo-GPU-QuadroP400-x86_64-Debug-All-Direct3D
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1156596
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Kaylee Lubick <kjlubick@google.com>