Revert "give jenkins/java more memory"

This reverts commit 16a1e225.

Ebourg said this wasn't really needed…

hosts/jenkins/etc/default/jenkins

@@ -8,7 +8,7 @@ JAVA=/usr/bin/java
 
 # arguments to pass to java
 #JAVA_ARGS="-Xmx512m"  # + MaxPermSize is 128m normally
-JAVA_ARGS="-Xmx4096m -XX:MaxPermSize=384m"
+JAVA_ARGS="-Xmx3072m -XX:MaxPermSize=384m"
 #JAVA_ARGS="-Djava.net.preferIPv4Stack=true" # make jenkins listen on IPv4 address
 
 PIDFILE=/var/run/jenkins/jenkins.pid