Remove u#-grapheme-len modules as too redundant with u#-grapheme-next.

Remove u#-grapheme-len modules as too redundant with u#-grapheme-next.

Remove module 'u8-grapheme-len' as too redundant with
'u8-grapheme-next'.
* modules/unigbrk/u8-grapheme-len: Delete file.
* modules/unigbrk/u8-grapheme-len-tests: Delete file.
* lib/unigbrk.in.h: Remove prototype for deleted function.
* lib/unigbrk/u8-grapheme-len.c: Delete file.
* tests/unigbrk/test-u8-grapheme-len.c: Delete file.

Remove module 'u16-grapheme-len' as too redundant with
'u16-grapheme-next'.
* modules/unigbrk/u16-grapheme-len: Delete file.
* modules/unigbrk/u16-grapheme-len-tests: Delete file.
* lib/unigbrk.in.h: Remove prototype for deleted function.
* lib/unigbrk/u16-grapheme-len.c: Delete file.
* tests/unigbrk/test-u16-grapheme-len.c: Delete file.

Remove module 'u32-grapheme-len' as too redundant with
'u32-grapheme-next'.
* modules/unigbrk/u32-grapheme-len: Delete file.
* modules/unigbrk/u32-grapheme-len-tests: Delete file.
* lib/unigbrk.in.h: Remove prototype for deleted function.
* lib/unigbrk/u32-grapheme-len.c: Delete file.
* tests/unigbrk/test-u32-grapheme-len.c: Delete file.

Suggested by Bruno Haible.