This reverts commit b19d123f.

Reason for revert: It breaks the more important change: https://chromium-review.googlesource.com/c/v8/v8/+/1042145
(Because it adds mutable objects to RO_SPACE).

Original change's description:
> [heap] Move even more objects into RO_SPACE
> 
> Moves all Oddballs, empty_feedback_metadata, lots of symbols and
> immortal heap numbers and several other empty collection objects.
> 
>       RO_SPACE  NEW_SPACE  OLD_SPACE  CODE_SPACE  MAP_SPACE  LO_SPACE
> old      31592          0     221160       33280        176         0
> new      35016          0     217736       33280        176         0
> diff     +3424                 -3424
> 
> Bug: v8:7464
> Change-Id: Ic99411bcbcb9c9a48b33c59dddb68359278fb0b3
> Reviewed-on: https://chromium-review.googlesource.com/1025996
> Commit-Queue: Dan Elphick <delphick@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#53053}

TBR=hpayer@chromium.org,mlippautz@chromium.org,delphick@chromium.org

Change-Id: Ieb81f88fe348fcffb67c153c0b116670318814f5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7464
Reviewed-on: https://chromium-review.googlesource.com/1049555Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53056}