kconfig: remove '---help---' support

The conversion is done. No more user of '---help---'.

Cc: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/kconfig/lexer.l

@@ -105,7 +105,7 @@ n	[A-Za-z0-9_-]
 "endchoice"		return T_ENDCHOICE;
 "endif"			return T_ENDIF;
 "endmenu"		return T_ENDMENU;
-"help"|"---help---"	return T_HELP;
+"help"			return T_HELP;
 "hex"			return T_HEX;
 "if"			return T_IF;
 "imply"			return T_IMPLY;