Update comment about allowing GUCs to change scanning.

Reported-by: David G. Johnston

Discussion: CAKFQuwZZvnxwSq9tNtvL+uyuDKGgV91zR_agtPxQHRWMWQRP8g@mail.gmail.com

src/backend/parser/scan.l

@@ -55,8 +55,7 @@ fprintf_to_ereport(const char *fmt, const char *msg)
  * GUC variables.  This is a DIRECT violation of the warning given at the
  * head of gram.y, ie flex/bison code must not depend on any GUC variables;
  * as such, changing their values can induce very unintuitive behavior.
- * But we shall have to live with it as a short-term thing until the switch
- * to SQL-standard string syntax is complete.
+ * But we shall have to live with it until we can remove these variables.
  */
 int			backslash_quote = BACKSLASH_QUOTE_SAFE_ENCODING;
 bool		escape_string_warning = true;