Refactor: various: Remove unnecessary SUPPORT_COROSYNC guards

For readability. Of note, is_corosync_cluster() can be used even without
SUPPORT_COROSYNC.

We recently put guards around is_corosync_cluster() in 192878b but on
second thought, it's more readable if we drop them where possible.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>