Fix checkstyle errors in teamcity

Change-Id: Ib74a9e3f9363391015ca51fead607be7820ba7c5
Reviewed-on: http://gerrit.dmdirc.com/2582
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Chris Smith <chris@dmdirc.com>

checkstyle/dmdirc_checks.xml

@@ -136,7 +136,6 @@
 
         <!-- Checks for common coding problems               -->
         <!-- See http://checkstyle.sf.net/config_coding.html -->
-        <module name="DoubleCheckedLocking"/>
         <module name="EmptyStatement"/>
         <module name="EqualsHashCode"/>
         <module name="HiddenField">