HADOOP-14367. Remove unused setting from pom.xml. Contributed by Chen Liang.

hadoop-project/pom.xml

@@ -90,7 +90,6 @@
     <findbugs.version>3.0.0</findbugs.version>
     <spotbugs.version>3.1.0-RC1</spotbugs.version>
 
-    <tomcat.version>6.0.48</tomcat.version>
     <guice.version>4.0</guice.version>
     <joda-time.version>2.9.4</joda-time.version>