home-assistant: Remove Matrix integration

The _hatch.chat_ Matrix homeserver is being retired.  We don't use
Matrix for any notifications any more.

home-assistant/configuration.yaml

@@ -75,25 +75,7 @@ light:
   - light.light_6
   - light.light_7
 
-matrix:
-  homeserver: https://hatch.chat
-  username: '@homeassistant:hatch.chat'
-  password: !secret matrix_password
-  rooms:
-  - '!DdgnpVhlRqeTeNqSEM:hatch.chat'
-  - '!oyDXJxjUeJkEFshmAn:hatch.chat'
-  commands:
-  - word: snapshot
-    name: snapshot
-  - word: bunnies
-    name: bunnies
-  - expression: 'lights (?P<scene>.*)'
-    name: lights
-
 notify:
-- platform: matrix
-  name: matrix
-  default_room: '!DdgnpVhlRqeTeNqSEM:hatch.chat'
 - platform: group
   name: mobile_apps_group
   services: