Revert "Fix Windows external texture interference (#25193)" (#25292)

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 d6e59460.

shell/platform/windows/external_texture_gl.cc

@@ -125,7 +125,6 @@ bool ExternalTextureGL::CopyPixelBuffer(size_t& width, size_t& height) {
   gl.glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, pixel_buffer->width,
                   pixel_buffer->height, 0, GL_RGBA, GL_UNSIGNED_BYTE,
                   pixel_buffer->buffer);
-  gl.glBindTexture(GL_TEXTURE_2D, 0);
   return true;
 }