graphlog: remove unused ASCIIDATA constant

It was introduced by d9acbe7b0049, returned by asciiformat() but never
read anywhere. 20140c249e63 stopped using it completely, and the
graphmod.CHANGESET type is passed through all functions.

hgext/graphlog.py

@@ -21,8 +21,6 b' cmdtable = {}'
 command = cmdutil.command(cmdtable)
 testedwith = 'internal'
 
-ASCIIDATA = 'ASC'
-
 def asciiedges(type, char, lines, seen, rev, parents):
     """adds edge info to changelog DAG walk suitable for ascii()"""
     if rev not in seen:
@@ -132,7 +130,7 b' def ascii(ui, state, type, char, text, c'
       - ui to write to
       - Somewhere to keep the needed state in (init to asciistate())
       - Column of the current node in the set of ongoing edges.
-      - Type indicator of node data == ASCIIDATA.
+      - Type indicator of node data, usually 'C' for changesets.
       - Payload: (char, lines):
         - Character to use as node's symbol.
         - List of lines to display as the node's text.