Only java_g supports the -l<number> flag, but it's in java's usage message

The -l<number> option (turn on logging at level <number>) is only recognized
by java_g, but it appears in java's usage message. -l<number> support is compiled
in only #ifdef LOGGING in javai.g, and LOGGING is apparently not defined when
building the normal java executable.

The description field as copied from bug report 1211345 follows:

The usage message of java and java_g both show a -l<number> option, although
that's only implemented for java. This might have been reported before, but I've
fixed it this time -- the option should only show up in java_g's usage message.