websites/d&t.com: drop obsolete formsubmit config

The *dustinandtabitha.com* website no longer uses *formsubmit* (the time
for RSVP has **long** passed).  Removing the configuration so the
file encrypted with Ansible Vault can go away.

roles/websites/dustinandtabitha.com/vars/main.yml

@@ -1,10 +0,0 @@
-dustinandtabitha_formsubmit:
-  csvfile: /srv/www/dustinandtabitha/data/rsvp.csv
-  defaults:
-    adult: 0
-    preschool: 0
-    school: 0
-  matrix:
-    homeserver: hatch.chat
-    room: '!qJoqJkHxCHgDSTZwwX:hatch.chat'
-    access_token: '{{ dustinandtabitha_formsubmit_matrix_token }}'