Deleted line that was not being used and causing a crash on C&U screen

Deleted code that was setting 'interval' local variable that was not even being used in the method and was causing a crash when changing a value in "Group By" pull down on Host C&U screen when there is no C&U data available for the chosen group, it is mostly happening on the fresh appliance.

https://bugzilla.redhat.com/show_bug.cgi?id=1123195
https://bugzilla.redhat.com/show_bug.cgi?id=1127765

@dclarizio please review/test.