Clean the perfDir after a successful build

archive/org.eclipse.wtp.releng/buildAll.xml

@@ -300,6 +300,7 @@
                 <delete dir="${buildDirectory}" failonerror="false"/>
                 <delete dir="${build.home}/${build.current}-${buildType}" failonerror="false"/>
                 <delete dir="${testDir}" failonerror="false"/>
+                <delete dir="${perfDir}" failonerror="false"/>
         </target>