parser: deprecate %error-verbose

It is unfortunate that %error_verbose was properly diagnosed as
obsoleted by "%define parse.error verbose", but %error-verbose was
not.

* src/parse-gram.y (%error-verbose): Remove support.
* src/scan-gram.l: Do it here instead, with a warning.
* tests/input.at (Deprecated directives): Check it.

src/parse-gram.y

@@ -143,7 +143,6 @@
   PERCENT_DEFAULT_PREC    "%default-prec"
   PERCENT_DEFINE          "%define"
   PERCENT_DEFINES         "%defines"
-  PERCENT_ERROR_VERBOSE   "%error-verbose"
   PERCENT_EXPECT          "%expect"
   PERCENT_EXPECT_RR       "%expect-rr"
   PERCENT_FLAG            "%<flag>"
@@ -290,12 +289,6 @@ prologue_declaration:
       defines_flag = true;
       spec_defines_file = xstrdup ($2);
     }
-| "%error-verbose"
-    {
-      muscle_percent_define_insert ("parse.error", @1, muscle_keyword,
-                                    "verbose",
-                                    MUSCLE_PERCENT_DEFINE_GRAMMAR_FILE);
-    }
 | "%expect" INT                    { expected_sr_conflicts = $2; }
 | "%expect-rr" INT                 { expected_rr_conflicts = $2; }
 | "%file-prefix" STRING            { spec_file_prefix = $2; }