Revert of Only use FreeSpace objects in the free list. (patchset #3 id:40001 of https://codereview.chromium.org/876613002/)

Reason for revert:
Test failures

Original issue's description:
> Only use FreeSpace objects in the free list.
>
> This solves an issue with the custom startup snapshot, in cases where
> deserializing the isolate requires more than one page per space.
>
> R=hpayer@chromium.org
>
> Committed: https://crrev.com/66964395108f03220cb6f45ddc73c5965e2c76a9
> Cr-Commit-Position: refs/heads/master@{#26285}

TBR=hpayer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/882443004

Cr-Commit-Position: refs/heads/master@{#26287}