Remove PMD rules for empty constructors.

Dagger requires @Inject annotated blank constructors in some
cases, which our PMD rules are complaining about.

Change-Id: I969b974c91cc5faacb6a95daabc2567322293fd3
Reviewed-on: http://gerrit.dmdirc.com/2646
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>