Don't use FILE_SYSTEM_CASE in MS-DOS, or anywhere else.

Don't use FILE_SYSTEM_CASE in MS-DOS, or anywhere else.

 src/s/msdos.h (FILE_SYSTEM_CASE): Don't define.
 src/fileio.c (FILE_SYSTEM_CASE): Don't define.
 (Ffile_name_directory, Fexpand_file_name): Don't use FILE_SYSTEM_CASE.
 Fixes problems on MS-DOS with Vtemp_file_name_pattern when
 call-process-region passes it through expand-file-name.
 src/dired.c (file_name_completion): Don't use FILE_SYSTEM_CASE.
 admin/CPP-DEFINES: Remove FILE_SYSTEM_CASE.