[TASK] Clean up code of available services report

The code of the available services report contains a number of
incomplete phpDoc blocks plus some small variables initialization
errors. This should be corrected before further work.

Change-Id: I02470e4daecfb8dd15e9477f33ba4023e0340c08
Resolves: #31174
Releases: 4.6
Reviewed-on: http://review.typo3.org/6170
Reviewed-by: Francois Suter
Tested-by: Francois Suter