Default JMC binaries should not hardcode -vm /usr/bin/java

This is related to JMC-6314. Current jmc.ini hardcodes /usr/bin/java as the go-to JVM to run with. However, it expects Flight Recorder to be available in that JVM and it also --add-modules lots of stuff. That means unless the default Java is 11 on the system, default JMC would not start. 

I suggest we drop "-vm /usr/bin/java" from jmc.ini and let it start with the Java available on PATH, which may be pointed to 11 binaries explicitly for JMC.