Refactor: libcrmcluster: avoid unnecessary function

Previously, pcmk__corosync_connect() (recently renamed from
init_cs_connection()) would call init_cs_connection_once(), retrying under
certain conditions.

However, init_cs_connection_once() returned a gboolean TRUE/FALSE result, while
pcmk__corosync_connect() intepreted it as an integer CS_* code. Coincidentally,
CS_OK == TRUE, so it worked, but it could never hit the retry code.

Now, pcmk__corosync_connect() has essentially become init_cs_connection_once(),
which no longer exists. Retrying is not attempted.