missing_type: char16_t and char32_t are always defined in uchar.h since C11

Now, we use C17, hence the fallback definitions can be dropped.

src/basic/escape.h

@@ -8,7 +8,6 @@
 #include <uchar.h>
 
 #include "string-util.h"
-#include "missing_type.h"
 
 /* What characters are special in the shell? */
 /* must be escaped outside and inside double-quotes */

src/basic/missing_type.h

@@ -1,12 +0,0 @@
-/* SPDX-License-Identifier: LGPL-2.1-or-later */
-#pragma once
-
-#include <uchar.h>
-
-#if !HAVE_CHAR32_T
-#  define char32_t uint32_t
-#endif
-
-#if !HAVE_CHAR16_T
-#  define char16_t uint16_t
-#endif

src/basic/utf8.h

@@ -7,7 +7,6 @@
 #include <uchar.h>
 
 #include "macro.h"
-#include "missing_type.h"
 
 #define UTF8_REPLACEMENT_CHARACTER "\xef\xbf\xbd"
 #define UTF8_BYTE_ORDER_MARK "\xef\xbb\xbf"