bug#45700: rm should not prompt if ! isatty(2)

[John Wiersba]

$ /bin/rm --version
rm (GNU coreutils) 8.30

$ uname -a
Linux xxx 5.4.0-59-generic #65-Ubuntu SMP Thu Dec 10 12:01:51 UTC 2020 x86_64 
x86_64 x86_64 GNU/Linux

$ lsb_release -a
No LSB modules are available.
Distributor ID:    Linuxmint
Description:    Linux Mint 20
Release:    20
Codename:    ulyana

$ touch asdf && chmod a-w asdf && rm asdf 2>&1 | catrm: remove write-protected 
regular empty file 'asdf'?          # should *not* prompt

If the prompt cannot be seen, then it can't be properly answered, so there is 
no point in prompting and consequently leaving the user with a hanging command 
and no way to know what's being expected of them.  Instead rm should attempt to 
remove the file and succeed or fail based on the result.  Same for any other 
commands (mv, cp) in similar situations.

I know about the options -f and --interactive=never, but they shouldn't be 
needed in this case.

Thanks!