Don't print greetings in interactive read in fake-interactive shell

If a user passes "-i" when running a script, they ought to expect
weird behavior i.e. fish might run the user's interactive-only
configuration which might print things to TTY etc.  But at least
for our part of the configuration, we can avoid depending on the
user-settable interactive bit.

__fish_config_interactive is already only called when we paint the
first prompt, either for a prompt (which implies we're an interactive
shell) or for builtin read (which does not imply anything about the
interactivity of the shell).

Only print greetings when not in interactive read. Notably, "status
is-interactive-read" is not overridable by the user.

This helps us get rid of more "status is-interactive" switches.