We remove Raft documentation irrelevant in 5.5.
One of the changes is removing a part of the "Enabling Raft" section
in raft.rst. Since Raft is mandatory in 5.5, the only way to enable
it in this version is by performing a rolling upgrade from 5.4. We
only need to have this case well-documented. In particular, we
remove information that also appears in the upgrade guides like
verifying schema synchronization.
Similarly, we remove a sentence from the "Manual Recovery Procedure"
section in handling-node-failures.rst because it mentions enabling
Raft manually, which is impossible in 5.5.
The rest of the changes are just removing information about
checking or setting consistent_cluster_management, which has become
unused.
f23f8628b7
