Revert of Add gpu implementation of OverdrawXfermode (patchset #6 id:100001 of https...

Revert of Add gpu implementation of OverdrawXfermode (patchset #6 id:100001 of https://codereview.chromium.org/1607253002/ )

Reason for revert:
Overdraw Xfer mode using new fangled glsl features

Original issue's description:
> Add gpu implementation of OverdrawXfermode
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1607253002
>
> Committed: https://skia.googlesource.com/skia/+/8bc3cf88bbf5e5d5724356f076931bb70a6117ba

TBR=egdaniel@google.com
# Not skipping CQ checks because original CL landed more than 1 days ago.

Review URL: https://codereview.chromium.org/1626443002