memctx: simplify _manifest with new revlog nodeids

This was originally written before we had modifiednodeid and
addednodeid, so we had to get the parents of the context, the data from
the function, and then hash that.

This is much more simple now and helps refactor more code later.

mercurial/context.py

@@ -36,7 +36,6 b' from . import ('
     phases,
     pycompat,
     repoview,
-    revlog,
     scmutil,
     sparse,
     subrepo,
@@ -2287,17 +2286,10 b' class memctx(committablectx):'
         man = pctx.manifest().copy()
 
         for f in self._status.modified:
-            p1node = nullid
-            p2node = nullid
-            p = pctx[f].parents() # if file isn't in pctx, check p2?
-            if len(p) > 0:
-                p1node = p[0].filenode()
-                if len(p) > 1:
-                    p2node = p[1].filenode()
-            man[f] = revlog.hash(self[f].data(), p1node, p2node)
+            man[f] = modifiednodeid
 
         for f in self._status.added:
-            man[f] = revlog.hash(self[f].data(), nullid, nullid)
+            man[f] = addednodeid
 
         for f in self._status.removed:
             if f in man: