remove the isatty() call so it's easier to audit the helper

remove the isatty() call so it's easier to audit the helper

The isatty() check is just to catch users poking around; it provides little or no real security. With this change, you can do stuff like

$ /usr/libexec/polkit-grant-helper-pam
davidz
PAM_PROMPT_ECHO_OFF Password:
<enter real password here>
SUCCESS

$ /usr/libexec/polkit-grant-helper-pam
davidz
PAM_PROMPT_ECHO_OFF Password:
not_my_password
polkit-grant-helper-pam: pam_authenticated failed: Authentication failure
FAILURE

which is useful for auditing.