Revert "mon: when electing, be sure acked leaders have new enough stores to lead"

This was somehow broken -- out-of-date leaders were being elected -- and
we've decided smaller band-aids are more appropriate. We don't completely
revert the MMonElection changes, though -- there have been user clusters
running the code which includes these messages so we can't pretend it
never happened. We can make them clearly unused in the code, though.

This reverts commit fcaabf1a22723c571c10d402464071c6405607c0.

Signed-off-by: Greg Farnum <greg@inktank.com>
Revert "mon: update assert for looser requirements"

We reverted the gating by paxos sequences, so now we don't
need to look at them at all.

This reverts commit 1e6f02b337767012aeb387da9582cd7ad5a03084.
Signed-off-by: Greg Farnum <greg@inktank.com>
mon: if we get our own sync_start back, drop it on the floor.

We have timeouts that will clean everything up, and this can happen
in some cases that we've decided are legitimate. Hopefully we'll
be able to do something else later.

Signed-off-by: Greg Farnum <greg@inktank.com>
mon: Monitor: disregard paxos_max_join_drift when deciding whether to sync

We should only rely on whether our paxos version is overlap with whatever
they have -- we'll catch up later with them.

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
Merge branch 'wip-4837-election-syncing' into next

Reviewed-by: Sage Weil <sage@inktank.com>