This reverts commit 5db04cc0.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Revert "[regexp] Only append to JSRegExpResult's initial map if we add descriptor"
> 
> This reverts commit dc1cc223.
> 
> Revert "[regexp] Implement the match indices proposal"
> 
> This reverts commit 9460101c.
> 
> Reason for revert: Causes confusion on Blink side, as it introduces
> an object with >=2 internal fields that is not a wrapper (see bug).
> 
> Bug: chromium:996681
> Change-Id: I5c167e9e15bfbec2aa6b843e3063ead5d52fb26c
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1768897
> Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#63376}

TBR=yangguo@chromium.org,sigurds@chromium.org,joshualitt@chromium.org

Change-Id: Ic58fc3fc83faaf86bd895da29eacb7d51c443beb
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:996681
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1768584Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63379}