(add-to-diary-list): Fix typo in previous doc fix.

lisp/calendar/diary-lib.el

@@ -332,7 +332,7 @@ The function takes a string argument and must return a string.")
 Do nothing if DATE or STRING is nil.  DATE is the (MONTH DAY
 YEAR) for which the entry applies; STRING is the text of the
 entry as it will appear in the diary (i.e. with any format
-strings such as \%d\" expanded); SPECIFIER is the date part of
+strings such as \"%d\" expanded); SPECIFIER is the date part of
 the entry as it appears in the diary-file; LITERAL is the entry
 as it appears in the diary-file (i.e. before expansion).  If
 LITERAL is nil, it is taken to be the same as STRING.