This reverts commit ad1fcd43.

Reason for revert: Breaks waterfall.

Original change's description:
> [cleanup] Remove the now-unused deopt_count from feedback vector.
> 
> Bug: v8:9183
> Change-Id: Iceeccc8ab1e4e77b428e7e2feec39bff3317f241
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1617675
> Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#61665}

TBR=mstarzinger@chromium.org,jarin@chromium.org

Change-Id: Iea0e6a329f55a3a941f0b976925b2abdf7eece38
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:9183
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1619867Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61666}