Reject ProposeRaftCommand from removed replicas

[bdarnell]

When a replica of a gossiped range is removed, the gossip goroutines may persist after the removal, and call ProposeRaftCommand. This will recreate the group in raft and hang the goroutine indefinitely. Store.ProposeRaftCommand should reject any commands for ranges that are not in the current Store.ranges map.

Discovered in #1928.

[tbg]

is this still current?

[bdarnell]

Fixed yesterday in #2893