Remove GFS2_HAS_LH_V2 conditionals
    
    Our own gfs2_ondisk.h has v2 log headers so there's no need for these
    conditionals. There aren't any users of gfs2_log_header_v1_*() functions
    so fold those into gfs2_log_header*().
    
    Signed-off-by: Andrew Price <anprice@redhat.com>