Revert of Move instanced index buffer creation to flush time (patchset #6 id:100001 of https://codereview.chromium.org/1116943004/)

Reason for revert:
messed up caching, recreating index buffers all the time.

Original issue's description:
> Move instanced index buffer creation to flush time
>
> Committed: https://skia.googlesource.com/skia/+/ab622c7b8cc8c39f0a594e4392b9e31b7e1ddb26

TBR=joshualitt@google.com,robertphillips@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1126613003
26 files changed