qa/suites/fs/workload: drop mgrmodules stanza

qa/suites/fs/workload: drop mgrmodules stanza

After commit 5601f91bf97e ("qa: move some configs to cluster-conf"),
mgrmodules shouldn't be needed.  Currently "ceph mgr module enable"
command actually gets run twice with the one triggered by mgrmodules
coming in 10 minutes later:

2024-07-04T02:37:06.207 INFO:tasks.cephadm:enabling module snap_schedule
2024-07-04T02:37:06.208 DEBUG:teuthology.orchestra.run.smithi032:> sudo /home/ubuntu/cephtest/cephadm ... shell ... -- sudo ceph --cluster ceph mgr module enable snap_schedule

2024-07-04T02:47:08.104 INFO:teuthology.run_tasks:Running task sequential...
2024-07-04T02:47:08.114 INFO:teuthology.task.sequential:In sequential, running task sequential...
2024-07-04T02:47:08.114 INFO:teuthology.task.sequential:In sequential, running task print...
2024-07-04T02:47:08.115 INFO:teuthology.task.print:Enabling mgr modules
2024-07-04T02:47:08.115 INFO:teuthology.task.sequential:In sequential, running task exec...
2024-07-04T02:47:08.116 INFO:teuthology.task.exec:Executing custom commands...
2024-07-04T02:47:08.116 INFO:teuthology.task.exec:Running commands on role mon.a host ubuntu@smithi032.front.sepia.ceph.com
2024-07-04T02:47:08.116 DEBUG:teuthology.orchestra.run.smithi032:> sudo TESTDIR=/home/ubuntu/cephtest bash -c 'ceph mgr module enable snap_schedule'

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>