shaped-texture: Do not invalidate content on set_cogl_texture()

This was wrongly introduced in 75cffd0ec4. As the comment above explains, we
only want to queue redraws in response to surface/buffer damage.

This triggered a full redraw when using DMA buffers on Wayland as we currently
create a new texture on every buffer_attach(), breaking partial invalidation.

Fixes https://gitlab.gnome.org/GNOME/mutter/issues/947

src/compositor/meta-shaped-texture.c

@@ -495,8 +495,6 @@ set_cogl_texture (MetaShapedTexture *stex,
 
   if (stex->create_mipmaps)
     meta_texture_tower_set_base_texture (stex->paint_tower, cogl_tex);
-
-  clutter_content_invalidate (CLUTTER_CONTENT (stex));
 }
 
 static gboolean