os/fs.c: remove os_file_is_readonly()

os_file_is_readonly() in its current form is equivalent to
!os_file_is_writable(). This does not appear to be a bug, because Vim's
use of check_file_readonly() (which we changed to os_file_is_readonly())
is equivalent to !os_file_is_writable() in every case.

os_file_is_readonly() also fails this test:

    returns false if the file is non-read, non-write

A more useful form would define behavior under these cases:

  - path is executable (but not writable)
  - path is non-existent
  - path is directory

But there is no reason for os_file_is_readonly() to exist, so remove it.

0 files changed, 0 insertions, 0 deletions