dutil: Untabify, to pacify gcc
    
    dutil.c: In function 'rng_validate':
    dutil.c:324:5: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
         if (r != 0 && ncf->errcode == NETCF_NOERROR)
         ^~
    dutil.c:328:2: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'if'
      xmlRelaxNGFreeValidCtxt(ctxt);
      ^~~~~~~~~~~~~~~~~~~~~~~
    
    The warning is caused because the 'if' was indented with four spaces,
    while the 'xmlRelaxNGFreeValidCtxt' was indented with TAB; and gcc
    couldn't figure out that we were asking for TAB to represent 4 instead
    of 8 spaces.  Rather than add more TABs, I'd rather nuke them all.
    
    Patch best viewed with 'git diff -b'.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>