log: remove func loc info unless MM_LOG_FUNC_LOC is defined

The user can build the project passing custom CFLAGS to enable the
function location information, e.g.:

    $ ./configure --prefix=/usr CFLAGS="-DMM_LOG_FUNC_LOC"

src/mm-log.h

@@ -53,7 +53,6 @@ gboolean mm_log_setup (const char *level,
                        const char *log_file,
                        gboolean show_ts,
                        gboolean rel_ts,
-                       gboolean debug_func_loc,
                        GError **error);
 
 void mm_log_shutdown (void);