convert: remove incorrect and unused handling of removed svn directories

Since it was introduced in f0c58fd4b798, tidy_dirs has been comparing
the result of os.listdir with a string - which never can be true.
Convert apparently works anyway and there is no test coverage of it.

It also seems like it could make a bigger difference on older svn versions but
is less relevant with more recent versions.

Instead of trying to fix the code, we take the low risk option and remove it.

hgext/convert/subversion.py

@@ -1211,16 +1211,6 b' class svn_sink(converter_sink, commandli'
             self.xargs(files, 'add', quiet=True)
         return files
 
-    def tidy_dirs(self, names):
-        deleted = []
-        for d in sorted(self.dirs_of(names), reverse=True):
-            wd = self.wjoin(d)
-            if os.listdir(wd) == '.svn':
-                self.run0('delete', d)
-                self.manifest.remove(d)
-                deleted.append(d)
-        return deleted
-
     def addchild(self, parent, child):
         self.childmap[parent] = child
 
@@ -1258,7 +1248,6 b' class svn_sink(converter_sink, commandli'
                 self.manifest.remove(f)
             self.delete = []
         entries.update(self.add_files(files.difference(entries)))
-        entries.update(self.tidy_dirs(entries))
         if self.delexec:
             self.xargs(self.delexec, 'propdel', 'svn:executable')
             self.delexec = []