Revert "[scenic] Add SetClipPlanesCmd."

This reverts commit 18e350de44581d0150d9b9ea07294c336bdc8c7e.

Reason for revert: Breaks clients of old SDK (Chromium)

Original change's description:
> [scenic] Add SetClipPlanesCmd.
>
> Scenic is moving away from stencil-buffer clipping; instead
> clients will specify a list of clip planes which apply to a
> node and all of its children.  This CL adds the API, but does
> not yet implement it (i.e. content will not yet be clipped to
> the specified volume).
>
> TEST=no-op; API not yet called nor implemented.
>
> Change-Id: I8ec52752d20c0c5b21ec8722c39dee71d92ba271

TBR=jjosh@google.com,mikejurka@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: Ia232a237d0174310bbd4181f4201c8dfcba7ea31
7 files changed