xfstests: cleanup the codes related to h_chksum

xfstests: cleanup the codes related to h_chksum

From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>

  Since h_chksum field has gone away, we should cleanup the related codes

    [CC]    loggen
loggen.c: In function 'loggen_unmount':
loggen.c:137:9: error: 'xlog_rec_header_t' has no member named 'h_chksum'
loggen.c: In function 'loggen_empty':
loggen.c:205:9: error: 'xlog_rec_header_t' has no member named 'h_chksum'

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>