fixes for compatibility with new checkstyle version

com.oracle.truffle.r.runtime/.checkstyle_checks.xml

@@ -101,7 +101,6 @@
       <property name="severity" value="ignore"/>
       <metadata name="net.sf.eclipsecs.core.lastEnabledSeverity" value="inherit"/>
     </module>
-    <module name="JUnitTestCase"/>
     <module name="ModifiedControlVariable"/>
     <module name="MutableException">
       <property name="severity" value="ignore"/>