files: msmtprc: remove allow_from_override

The version of msmtp on milliways doesn't recognise allow_from_override.

files/msmtprc

@@ -17,8 +17,6 @@ tls_starttls off
 from %U@%H
 #
 aliases /etc/aliases
-# Do not allow programs to override this envelope-from address via -f
-allow_from_override off
 # Always set a From header that matches the envelope-from address
 set_from_header on