Releng: use boot OT/J compiler to create new compiler for phase 2

- try updating instead of uninstall (which doesn't work for the patch)
diff --git a/releng/build-scripts/build/p2helper.xml b/releng/build-scripts/build/p2helper.xml
index 1341f22..4f09e00 100644
--- a/releng/build-scripts/build/p2helper.xml
+++ b/releng/build-scripts/build/p2helper.xml
@@ -70,30 +70,10 @@
         </java>
     </target>
 
-    <target name="uninstallFeature">
-        <echo message="Uninstalling ${feature}"/>
-        <java
-                inputstring=""
-                dir="${targetEclipseDir}"
-                fork="true"
-                classname="org.eclipse.equinox.launcher.Main"
-                classpath="${targetEclipseDir}/plugins/${org.eclipse.equinox.launcher_jar}">
-            <jvmarg value="-Declipse.p2.MD5Check=false" />
-            <arg value="-consoleLog"/>
-            <arg value="-application"/>
-            <arg value="org.eclipse.equinox.p2.director"/>
-            <arg value="-metadataRepository" />
-            <arg value="file:${sourceUpdatesDir}" />
-            <arg value="-artifactRepository" />
-            <arg value="file:${sourceUpdatesDir}" />
-            <arg value="-uninstallIU" />
-            <arg value="${feature}" />
-        </java>
-    </target>
-
     <target name="installOTDT">
     	<echo message="Installing the OTDT from ${otdtUpdatesDir} into ${test.eclipseDir}"/>
-        <antcall target="uninstallFeature">
+        <antcall target="installFeature">
+        	<!-- update -->
             <param name="feature" value="org.eclipse.objectteams.otdt.core.patch.feature.group"/>
             <param name="sourceUpdatesDir" value="${otdtUpdatesDir}"/>
             <param name="targetEclipseDir" value="${test.eclipseDir}"/>