Remove all references to buffer-file-type and related features.

Remove all references to buffer-file-type and related features.

 src/xdisp.c (decode_mode_spec): Remove handling of %t.

 lisp/net/ange-ftp.el (ange-ftp-insert-file-contents): Don't reference
 buffer-file-type.
 lisp/mail/feedmail.el (feedmail-force-binary-write): Doc fix.
 (feedmail-run-the-queue, feedmail-dump-message-to-queue)
 (feedmail-send-it-immediately): Don't bind buffer-file-type, bind
 coding-system-for-write instead.
 lisp/jka-compr.el (jka-compr-write-region): Don't bind
 buffer-file-type.
 lisp/emacs-lisp/bytecomp.el (byte-compile-file): Don't bind
 buffer-file-type.
 lisp/files.el (file-name-buffer-file-type-alist): Remove defvar.
 (insert-file-contents-literally): Remove reference to
 file-name-buffer-file-type-alist.
 lisp/dos-w32.el (file-name-buffer-file-type-alist): Deprecate and
 make-obsolete.
 (find-buffer-file-type-match, find-buffer-file-type): Remove.
 (find-buffer-file-type-coding-system): Remove references to
 find-buffer-file-type-match, find-buffer-file-type, and
 buffer-file-type.
 Don't put find-buffer-file-type-coding-system into
 file-coding-system-alist.
 (find-file-binary, find-file-text): Bind coding-system-for-read
 instead of file-name-buffer-file-type-alist.
 lisp/erc/erc-dcc.el (erc-dcc-get-file): Don't reference buffer-file-type.

 doc/emacs/msdog.texi (Text and Binary): Delete the description of
 file-name-buffer-file-type-alist.

 doc/lispref/modes.texi (%-Constructs): Remove the description of %t.
 doc/lispref/nonascii.texi (MS-DOS File Types): Delete node.

Fixes: debbugs:12989