Remove unnecessary #include of SkPromiseImageTexture (#42770)

I was refactoring this class on the Skia side and saw Flutter #included it, but did not appear to actually use it.

This replaces an unnecessary #include with a necessary one.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: kjlubick

lib/ui/snapshot_delegate.h

@@ -11,7 +11,7 @@
 #include "flutter/display_list/display_list.h"
 #include "third_party/skia/include/core/SkImage.h"
 #include "third_party/skia/include/core/SkPicture.h"
-#include "third_party/skia/include/core/SkPromiseImageTexture.h"
+#include "third_party/skia/include/gpu/GrBackendSurface.h"
 #include "third_party/skia/include/gpu/GrContextThreadSafeProxy.h"
 #include "third_party/skia/include/gpu/GrDirectContext.h"