maint: don't use mbsr?chr.

Basically, revert ba60c39547a445dee3e07920931b4d7a81843868's move to
mbs* functions, which was prompted by -DGNULIB_POSIXCHECK.  See
<http://lists.gnu.org/archive/html/bison-patches/2012-05/msg00052.html>
and following.

* bootstrap.conf: No longer ask for them.
* src/files.c, src/getargs.c, src/location.c,
* src/parse-gram.c, src/parse-gram.y, src/scan-gram.l,
* src/symtab.c: s/mbs(r?chr)/str$1/g.

src/symtab.c

@@ -67,7 +67,7 @@ symbol_new (uniqstr tag, location loc)
 
   /* If the tag is not a string (starts with a double quote), check
      that it is valid for Yacc. */
-  if (tag[0] != '\"' && tag[0] != '\'' && mbschr (tag, '-'))
+  if (tag[0] != '\"' && tag[0] != '\'' && strchr (tag, '-'))
     yacc_at (loc, _("POSIX Yacc forbids dashes in symbol names: %s"),
              tag);