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>

checkstyle/pmd_checks.xml

 <rule ref="rulesets/braces.xml/IfElseStmtsMustUseBraces"><priority>1</priority></rule>
 <rule ref="rulesets/braces.xml/ForLoopsMustUseBraces"><priority>1</priority></rule>
 
-<rule ref="rulesets/controversial.xml/UnnecessaryConstructor"><priority>1</priority></rule>
 <rule ref="rulesets/controversial.xml/UnusedModifier"><priority>1</priority></rule>
 <rule ref="rulesets/controversial.xml/DontImportSun"><priority>1</priority></rule>
 <rule ref="rulesets/controversial.xml/UnnecessaryParentheses"><priority>1</priority></rule>
 <rule ref="rulesets/design.xml/SimplifyConditional"><priority>1</priority></rule>
 <rule ref="rulesets/design.xml/UnnecessaryLocalBeforeReturn"><priority>1</priority></rule>
 <rule ref="rulesets/design.xml/NonThreadSafeSingleton"><priority>1</priority></rule>
-<rule ref="rulesets/design.xml/UncommentedEmptyConstructor"><priority>1</priority></rule>
 <rule ref="rulesets/design.xml/AvoidConstantsInterface"><priority>1</priority></rule>
 <rule ref="rulesets/design.xml/UnsynchronizedStaticDateFormatter"><priority>1</priority></rule>
 <rule ref="rulesets/design.xml/PreserveStackTrace"><priority>1</priority></rule>