migrate to new tlsserver Let's Encrypt profile

We can no longer use OCSP stapling and Must-Staple. These will soon be
obsolete once the `shortlived` profile is available for public use since
it will provide certificates with a similar lifetime as OCSP responses.

In the meantime, we've moved to the `tlsserver` profile stripping legacy
features to prepare for the `shortlived` profile which will be identical
to `tlsserver` but with a validity period of 6 days.

The certificate for SUPL is still temporarily using the classic profile
to work around the older generations of end-of-life Snapdragon Pixels
not having support for SNI. We can eventually drop support for these
devices from the SUPL service to allow us to disable TLSv1.1, DHE and
move to the `tlsserver` or `shortlived` profile.

The certificate for SMTP is still temporarily using the classic profile
to avoid potential compatibility issues with servers supporting TLSv1.2
but still not yet supporting SNI.

certbot/discuss.grapheneos.org

@@ -1,5 +1,5 @@
 certbot certonly --webroot --webroot-path /srv/certbot --no-eff-email \
-    --key-type ecdsa --reuse-key --must-staple \
-    --deploy-hook "certbot-ocsp-fetcher -o /var/cache/certbot-ocsp-fetcher" \
+    --key-type ecdsa --reuse-key --preferred-profile tlsserver \
+    --deploy-hook "nginx -s reload" \
     --cert-name discuss.grapheneos.org \
     -d discuss.grapheneos.org