Remove slim coding ruleset

Author: adriansuter

phpcs.xml.dist

@@ -10,7 +10,6 @@
     <!-- inherit rules from: -->
     <rule ref="PSR2"/>
     <rule ref="Generic.Arrays.DisallowLongArraySyntax"/>
-    <rule ref="../Slim-Coding-Standard/ruleset.xml"/>
 
     <!-- Paths to check -->
     <file>src</file>