revset: undocument wdir() until its command outputs get stable

wdir() implementation is still incomplete and shouldn't be advertised to
users. This patch will be backed out when

 - template values such as {rev} and {node} are settled
 - major commands and revsets work without crashing

mercurial/commands.py

@@ -267,9 +267,6 @@ def annotate(ui, repo, *pats, **opts):
     anyway, although the results will probably be neither useful
     nor desirable.
 
-    By default, annotate files in the parent of the working directory.
-    Use -r "wdir()" to annotate the working directory files.
-
     Returns 0 on success.
     """
     if not pats:

mercurial/revset.py

@@ -1898,10 +1898,8 @@ def user(repo, subset, x):
     """
     return author(repo, subset, x)
 
+# experimental
 def wdir(repo, subset, x):
-    """``wdir()``
-    Working directory.
-    """
     # i18n: "wdir" is a keyword
     getargs(x, 0, 0, _("wdir takes no arguments"))
     if None in subset: