Revert "HADOOP-19502. Add RegexpSingleline module to checkstyle.xml. (#7505) …" (#7534)

This reverts commit 488376c13b1b374159b07db55ace2e7edc265ac8.

hadoop-build-tools/src/main/resources/checkstyle/checkstyle.xml

@@ -73,11 +73,6 @@
         <property name="max" value="100"/>
     </module>
 
-    <module name="RegexpSingleline">
-        <property name="format" value="\s+$"/>
-        <property name="severity" value="warn"/>
-    </module>
-
     <module name="TreeWalker">
 
         <module name="SuppressWarningsHolder"/>