Revert "minigbm: introduce test allocation"

Revert "minigbm: introduce test allocation"

This reverts commit f0e607c7d436134b53fd45a4ead36d714451be8a.

Reason for revert: caused flaky regressions across the board.

BUG=b:150997559
Exempt-From-Owner-Approval: revert.

Original change's description:
> minigbm: introduce test allocation
>
> This change introduces a GBM_TEST_ALLOC flag to minigbm, which allows
> for the creation of fake buffers that can be used to determine buffer
> metadata without actually allocating a full buffer. The new flag is
> supported by the i915 backends. This flag also alleviates the need to
> cache buffers when virtio_gpu queries metadata properties.
>
> BUG=b:145994510
> TEST=play youtube with arcvm demo image plus this and virgl change
>
> Change-Id: I9c6819aa3b5b674e4bb33b0656f2a9f155b0884e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minigbm/+/1980688
> Tested-by: David Stevens <stevensd@chromium.org>
> Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
> Commit-Queue: David Stevens <stevensd@chromium.org>

Bug: b:145994510
Change-Id: I50079b7f0aabf38e1f373cac0f28c0e057eed760
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minigbm/+/2093923
Commit-Queue: Ilja H. Friedel <ihf@chromium.org>
Tested-by: Ilja H. Friedel <ihf@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>