emacs: reply: remove wrong sig/enc status buttons

emacs: reply: remove wrong sig/enc status buttons

This stops the (usually incorrect) sigstatus and encstatus buttons
appearing when replying in emacs, and updates the test suite to match.

Overriding the status button functions is a little unusual but much
less intrusive than passing an argument all the way down the call
chain. It also makes it clear exactly what it does.

We also hide the application/pgp-encrypted part as it can only contain
"Version: 1". We do this in notmuch show, which means it also happens
when replying.