cmdutil: stop tryimportone from using dirstateguard (BC)

There is no user of 'cmdutil.tryimportone()' other than
'commands.import_()', which can restore dirstate at failure of
applying patches by transaction or dirstateguard.

Therefore, it is reasonable to stop 'tryimportone()' from using
redundant 'dirstateguard', even though it changes behavior of
'tryimportone()'.

After this patch, 3rd party extensions should use 'dirstateguard' or
so explicitly, if they want to restore dirstate at failure of
importing a patch.

mercurial/cmdutil.py

@@ -890,7 +890,6 def tryimportone(ui, repo, hunk, parents
     msg = _('applied to working directory')
 
     rejects = False
-    dsguard = None
 
     try:
         cmdline_message = logmessage(ui, opts)
@@ -932,7 +931,6 def tryimportone(ui, repo, hunk, parents
 
         n = None
         if update:
-            dsguard = dirstateguard(repo, 'tryimportone')
             if p1 != parents[0]:
                 updatefunc(repo, p1.node())
             if p2 != parents[1]:
@@ -983,7 +981,6 def tryimportone(ui, repo, hunk, parents
                         extrapostimportmap[idfunc](repo[n])
                 finally:
                     repo.ui.restoreconfig(allowemptyback)
-            dsguard.close()
         else:
             if opts.get('exact') or opts.get('import_branch'):
                 branch = branch or 'default'
@@ -1021,7 +1018,6 def tryimportone(ui, repo, hunk, parents
             msg = _('created %s') % short(n)
         return (msg, n, rejects)
     finally:
-        lockmod.release(dsguard)
         os.unlink(tmpname)
 
 # facility to let extensions include additional data in an exported patch