Remove outdated and unused JAVA variable

`JAVACMD_OPTIONS` isn't actually used by osmosis or Java programs (`_JAVA_OPTIONS` is the proper variable):

    2014-10-08 21:14:24 import osmosis data
    2014-10-08 21:14:24   Picked up _JAVA_OPTIONS: -Dawt.useSystemAAFontSettings=on -Xms1024M -Xmx8g -XX:+UseConcMarkSweepGC -XX:+UseCompressedOops
    2014-10-08 21:14:24   Out 08, 2014 9:14:24 PM org.openstreetmap.osmosis.core.Osmosis run

We also shouldn't force a specific `Xms` or `Xmx` value (the user can and should set it based on his machine, like other Java options)