More timeout-related fixes. Remove last FIXMEs.

Bug: 33105915
Bug: 33463189

Don't actually evaluate HISTORY_MAIN_INDEX. We don't want a result
computed unless we already had the answer.

Use a fixed timeout for other history evaluations, since all such
evaluations end up getting queued on a single thread. Hence a short
timeout evaluation can end up waiting for a long timeout one. This
was hard to detect because of the original 10x timeout factor, but
became really apparent when I tried to decrease it.

Correctly propagate timeout information in collapse. Remove
clearMainPreservingTimeout, since we removed the only use.

Remove now obsolete FIXME comments.

Change-Id: Id2cc079f42757a363723f6ae3cbc59191bc418a3