dcache-webadmin, alarms: remove required annotations from datastore setters

For the profile "alarms-off", the placeholder datastore object is constructed without the following properties:

persistenceManagerFactory
alarmsCleanerEnabled
alarmsCleanerSleepInterval
alarmsCleanerSleepIntervalUnit
alarmsCleanerDeleteThreshold
alarmsCleanerDeleteThresholdUnit

However, the setters on these properties have the "@Required" annotation. This causes a fatal exception at startup.

Removing the annotations restores proper initialization.

(Once again I should have caught this regression, introduced in 6541).

Target: master
Require-notes: no
Require-book: no
Patch: http://rb.dcache.org/r/6572
Acked-by: Gerd