Remove writeResource down readPixels path
Remove writeResource down readPixels path

This is not needed and results in creating an empty command buffer.

Bug: angleproject:2818
Change-Id: I06e5542cb3cd819c18758c909b8fcb624b074874
Reviewed-on: https://chromium-review.googlesource.com/1232981
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Commit-Queue: Tobin Ehlis <c15ba1c6ec8841cd136fafb26b333b1f76c86fb4@google.com>

ppy/angle,ppy/angle,ppy/angle,ppy/angle