dirstatemap: move `_drop_entry` out of the common methods

Only the Python implementation uses it.

Differential Revision: https://phab.mercurial-scm.org/D12514

mercurial/dirstatemap.py

@@ -101,13 +101,6 b' class _dirstatemapcommon:'
     def _refresh_entry(self, f, entry):
         """record updated state of an entry"""
 
-    def _drop_entry(self, f):
-        """remove any entry for file f
-
-        This should also drop associated copy information
-
-        The fact we actually need to drop it is the responsability of the caller"""
-
     ### disk interaction
 
     def _opendirstatefile(self):
@@ -534,6 +527,11 b' class dirstatemap(_dirstatemapcommon):'
             self._map.pop(f, None)
 
     def _drop_entry(self, f):
+        """remove any entry for file f
+
+        This should also drop associated copy information
+
+        The fact we actually need to drop it is the responsability of the caller"""
         self._map.pop(f, None)
         self.copymap.pop(f, None)