This assertion had become nonsensical in #9915f0d0f104aa918c94340e9e47129b90421999.
It's from a time where the surrounding function was dealing with the
local store only.

Release note: None

Make checkCanReceiveLease() more nimble, anticipating broader use.

Release note: None

This patch backpedals a little bit on the logic introduced in cockroachdb#55148.
That patch said that, if a leader is known, every other replica refuses
to propose a lease acquisition. Instead, the replica in question
redirects whomever was triggering the lease acquisition to the leader,
thinking that the leader should take the lease.
That patch introduced a deadlock: some replicas refuse to take the lease
because they are not VOTER_FULL (see CheckCanReceiveLease()). To fix the
deadlock, this patch incorporates that check in the proposal buffer's
decision about whether or not to reject a proposal: if the leader is
believed to refuse to take the lease, then we again forward our own
lease request.

An edge case to the edge case is when the leader is not even part of the
proposer's range descriptor. This can happen if the proposer is far
behind. In this case, we assume that the leader is eligible. If it
isn't, the deadlock will resolve once the proposer catches up.

A future patch will relax the conditions under which a replica agrees to
take the lease. VOTER_INCOMING replicas should take the lease.
VOTER_DEMOTING are more controversial.

Fixes cockroachdb#57798

Release note: None