util: remove dead code which used to be for old python2 versions

Differential Revision: https://phab.mercurial-scm.org/D107

mercurial/util.py

@@ -295,16 +295,10 b' class digestchecker(object):'
 try:
     buffer = buffer
 except NameError:
-    if not pycompat.ispy3:
-        def buffer(sliceable, offset=0, length=None):
-            if length is not None:
-                return sliceable[offset:offset + length]
-            return sliceable[offset:]
-    else:
-        def buffer(sliceable, offset=0, length=None):
-            if length is not None:
-                return memoryview(sliceable)[offset:offset + length]
-            return memoryview(sliceable)[offset:]
+    def buffer(sliceable, offset=0, length=None):
+        if length is not None:
+            return memoryview(sliceable)[offset:offset + length]
+        return memoryview(sliceable)[offset:]
 
 closefds = pycompat.osname == 'posix'