qa/standalone/mon: remove --mon-inital-members setting

qa/standalone/mon: remove --mon-inital-members setting

Problem:

--mon-initial-members does nothing but causes monmap
to populate ``removed_ranks`` because the way we start
monitors in standalone tests uses ``run_mon $dir $id ..``
on each mon. Regardless of --mon-initial-members=a,b,c, if
we set --mon-host=$MONA,$MONB,$MONC (which we do every single tests),
everytime we run a monitor (e.g.,run mon.b) it will pre-build
our monmap with

```
noname-a=mon.noname-a addrs v2:127.0.0.1:7127/0,
b=mon.b addrs v2:127.0.0.1:7128/0,
noname-c=mon.noname-c addrs v2:127.0.0.1:7129/0,
```

Now, with --mon-initial-members=a,b,c we are letting
monmap know that we should have initial members name:
a,b,c, which we only have `b` as a match. So what
``MonMap::set_initial_members`` do is that it will
remove noname-a and noname-c which will
populate `removed_ranks`.

Solution:

remove all instances of --mon-initial-members
in the standalone test as it has no impact on
the nature of the tests themselves.

Fixes: https://tracker.ceph.com/issues/58132
Signed-off-by: Kamoltat <ksirivad@redhat.com>