bundle2: move the 'close' method off the unpackermixin

This method is unrelated to unpacking and only used by the unbundle20 class.
We move it there for clarity.

mercurial/bundle2.py

@@ -660,11 +660,6 b' class unpackermixin(object):'
                     raise
         return None
 
-    def close(self):
-        """close underlying file"""
-        if util.safehasattr(self._fp, 'close'):
-            return self._fp.close()
-
 def getunbundler(ui, fp, magicstring=None):
     """return a valid unbundler object for a given magicstring"""
     if magicstring is None:
@@ -817,6 +812,11 b' class unbundle20(unpackermixin):'
         self.params # load params
         return self._compressed
 
+    def close(self):
+        """close underlying file"""
+        if util.safehasattr(self._fp, 'close'):
+            return self._fp.close()
+
 formatmap = {'20': unbundle20}
 
 b2streamparamsmap = {}