[Partition Alloc] Remove dead comments.

An old form of a double-free check was present in comments. The new form is in
live code. Also remove a TODO we likely won't be able to do.

Bug: None
Change-Id: Ibbd18b6c98ae7729f46cf8f314e34b0634458d8c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1733803
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684173}
1 file changed