ceph-windows: actually disable the mgr for the vstart cluster

[tchaikov]

-WITH_MGR=OFF and -WITH_LTTNG=OFF were passed to do_cmake.sh with a single dash, so cmake never set them. The mgr has therefore been built and started by every vstart run since this script was added in 2022, only to fail loading rbd_support and telemetry because their python deps were never installed.

The librbd, rados and cephfs tests run against this cluster use the direct library API and do not need the mgr, so disable it as originally intended. Pass -DWITH_MGR=OFF (and -DWITH_LTTNG=OFF), and set CEPH_NUM_MGR=0 for vstart.sh so it does not try to start a ceph-mgr that is no longer built.

python3-prettytable is kept: it is a client CLI dependency (ceph_daemon.py), not a mgr one.

[tchaikov]

this change was inspired in following warning:

2026-06-24T13:37:19.349+0000 7f5613598640 -1 WARNING: all dangerous and experimental features are enabled.
2026-06-24T13:37:19.365+0000 7f5613598640 -1 WARNING: all dangerous and experimental features are enabled.
  cluster:
    id:     70dd019f-4195-4731-8eea-059b2e72b327
    health: HEALTH_WARN
            3 OSD(s) have BlueFS usage exceeding configured ratio of main device size
            Module 'rbd_support' has failed dependency: No module named 'dateutil'
            1 pool(s) do not have an application enabled
            3 pool(s) have no replicas configured
 
  services:
    mon: 3 daemons, quorum a,b,c (age 34m) [leader: a]
    mgr: x(active, since 34m)
    mds: 1/1 daemons up, 2 standby
    osd: 3 osds: 3 up (since 34m), 3 in (since 34m)
 
  data:
    volumes: 1/1 healthy
    pools:   5 pools, 257 pgs
    objects: 421 objects, 564 MiB
    usage:   3.6 GiB used, 14 GiB / 18 GiB avail
    pgs:     216 active+clean
             39  active+clean+snaptrim_wait
             2   active+clean+snaptrim

when investigating a windows test failure at https://jenkins.ceph.com/job/ceph-windows-pull-requests/81551/. which turns out to be a known issue tracked by https://tracker.ceph.com/issues/70847