Removes obsolete comment configuration from docs

Its-Jura does not use anymore the gerrit.config based commentOnXXX
configuration options and instead rely on the generic its-base 
rule-based actions. Leaving obsolete traces of the legacy config in
the its-jira plugin config is quite misleading and it is better to 
be removed.

Change-Id: Ia9b26f8904f0e740672f0e250e03ed0ba773e650