narrow: update TODO.rst now that we share format with sparse

The narrowspec format was unified with the sparse format in
f64ebe7d2259 (narrowspec: use sparse.parseconfig() to parse narrowspec
file (BC), 2018-08-03).

Differential Revision: https://phab.mercurial-scm.org/D4904

hgext/narrow/TODO.rst

@@ -9,9 +9,8 b' the stand-in to raise a ProgrammingError'
 Reason more completely about rename-filtering logic in
 narrowfilelog. There could be some surprises lurking there.
 
-Formally document the narrowspec format. Unify with sparse, if at all
-possible. For bonus points, unify with the server-specified narrowspec
-format.
+Formally document the narrowspec format. For bonus points, unify with the
+server-specified narrowspec format.
 
 narrowrepo.setnarrowpats() or narrowspec.save() need to make sure
 they're holding the wlock.