Revert of rename sk_gpu_test::GLContext to sk_gpu_test::GLTestContext (patchset #5 id:80001 of https://codereview.chromium.org/1849463002/ )

Reason for revert:
breaking bots

Original issue's description:
> rename sk_gpu_test::GLContext to sk_gpu_test::GLTestContext
>
> rename subclasses
>
> Fix up the EGL native GLTestContext
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1849463002
>
> TBR=jvanverth@google.com
>
> Committed: https://skia.googlesource.com/skia/+/4c7f0a16312c374eba4e8d5d46435ce9eb0b9971

TBR=jvanverth@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1850543003
34 files changed