remove comments on copyright status from UTF-8 implementation files

despite clarifications made to the COPYRIGHT file in commit
f0a61399, there continues to be
confusion about whether the permissions granted actually apply to all
files. I am the sole author of these files and clearly intend, and
have always intended, for the grant of permission to apply to them.

src/multibyte/internal.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include "internal.h"
 
 #define C(x) ( x<2 ? -1 : ( R(0x80,0xc0) | x ) )

src/multibyte/internal.h

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #define bittab __fsmu8
 
 #include <stdint.h>

src/multibyte/mblen.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include <stdlib.h>
 
 int mblen(const char *s, size_t n)

src/multibyte/mbrlen.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include <wchar.h>
 
 size_t mbrlen(const char *restrict s, size_t n, mbstate_t *restrict st)

src/multibyte/mbrtowc.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include <stdlib.h>
 #include <wchar.h>
 #include <errno.h>

src/multibyte/mbsinit.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include <wchar.h>
 
 int mbsinit(const mbstate_t *st)

src/multibyte/mbsnrtowcs.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include <wchar.h>
 
 size_t mbsnrtowcs(wchar_t *restrict wcs, const char **restrict src, size_t n, size_t wn, mbstate_t *restrict st)

src/multibyte/mbsrtowcs.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include <stdint.h>
 #include <wchar.h>
 #include <errno.h>

src/multibyte/mbtowc.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include <stdlib.h>
 #include <wchar.h>
 #include <errno.h>

src/multibyte/wcrtomb.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include <stdlib.h>
 #include <wchar.h>
 #include <errno.h>

src/multibyte/wcsnrtombs.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include <wchar.h>
 
 size_t wcsnrtombs(char *restrict dst, const wchar_t **restrict wcs, size_t wn, size_t n, mbstate_t *restrict st)

src/multibyte/wcsrtombs.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include <wchar.h>
 
 size_t wcsrtombs(char *restrict s, const wchar_t **restrict ws, size_t n, mbstate_t *restrict st)

src/multibyte/wctomb.c

-/* 
- * This code was written by Rich Felker in 2010; no copyright is claimed.
- * This code is in the public domain. Attribution is appreciated but
- * unnecessary.
- */
-
 #include <stdlib.h>
 #include <wchar.h>