Use KVAR in MS-Windows build, remove buffer-file-type.

Use KVAR in MS-Windows build, remove buffer-file-type.

 w32fns.c (Fx_create_frame): Use KVAR.
 w32term.c (w32_create_terminal): Use KVAR.
 s/ms-w32.h (MODE_LINE_BINARY_TEXT): Remove.
 xdisp.c (decode_mode_spec): Don't use MODE_LINE_BINARY_TEXT.
 fileio.c (Finsert_file_contents, Fwrite_region): Remove
 references to buffer_file_type.
 (syms_of_fileio): Don't intern and staticpro
 find-buffer-file-type.
 callproc.c (syms_of_callproc): Remove references to
 buffer_file_type.
 buffer.c (reset_buffer_local_variables): Don't set
 buffer_file_type.
 (init_buffer_once): Likewise.
 (syms_of_buffer): Don't define buffer-file-type.
 buffer.h (struct buffer): Remove buffer_file_type.