remove unneeded LOG_DEBUG when not compiling with DEBUG support

remove unneeded LOG_DEBUG when not compiling with DEBUG support

when ngircd is build without DEBUG enabled, LOG_DEBUG messages
are always discarded.

To avoid the extra code, ngircd has a LogDebug() wrapper which
gets removed by the compiler when compiling without DEBUG defined.

Update a few functings which were using the
Log(LOG_DEBUG, .. interface directly without #ifdef DEBUG guards.

   text	   data	    bss	    dec	    hex	filename
 127748	   1900	  28280	 157928	  268e8	ngircd.before
 126836	   1896	  28280	 157012	  26554	ngircd.after