libgfs2: Remove print_it extern requirement
    
    Now that libgfs2 doesn't depend on a print_it() function being provided
    by the utils, the extern declaration can be removed from libgfs2.h. The
    print_it functions in mkfs.gfs2 and gfs2_edit are moved into their
    struct_print.c files and made static. All other print_it definitions are
    removed or made static.
    
    Signed-off-by: Andrew Price <anprice@redhat.com>