rust: remove `atty` dependency
It is fully replaced with the now stable `std::io::IsTerminal` trait.
This was the last dependency flagged as a warning by `cargo audit`,
aside from `cpython` which we know about all too well: the plan is to
transition to PyO3 soon-ish.
#!/usr/bin/env python3
import errno
import os
import sys
for f in sys.argv[1:]:
try:
print(f, '->', os.readlink(f))
except OSError as err:
if err.errno != errno.EINVAL:
raise
print(f, '->', f, 'not a symlink')
sys.exit(0)