Revert "Fix Windows external texture interference (#25193)"

[cbracken]

This will cause the previous texture binding used by Skia to be
incorrectly unbound, such that should they need to re-used an existing
binding, we'll end up rendering blank instead.

Instead we should be using

context->flushAndSubmit();
context->resetContext(kAll_GrBackendState);

in EmbedderExternalTextureGL::ResolveTexture in order to notify Skia
that we've updated handles within the current binding and invalidate any
assumptions about previous modifications it has made to the context.

This reverts commit d6e5946.

Related flutter/flutter#78648

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