Remove hard-coded memory settings for 64bit Java 6

maxmem is no longer set for javac and javadoc in etc/local.properties.example.
Nor are these set by build.py. If the system is detected to be a 64 bit Java 6
VM, then no properties are set at all.

Otherwise, defaults are taken.

Note: my local environment had javac.maxmem set in ANT_OPTS which has likely
made this more complicated then it ever needed to be.