Remove |to_json causing trouble

Fixes a regression introduced in f6097fbba1, which was cauing Synapse
to die with this error message:

> ValueError: sender_localpart needs characters which are not URL encoded.

roles/matrix-bridge-mautrix-facebook/defaults/main.yml

@@ -107,7 +107,7 @@ matrix_mautrix_facebook_registration_yaml: |
       regex: '^@{{ matrix_mautrix_facebook_appservice_bot_username|regex_escape }}:{{ matrix_mautrix_facebook_homeserver_domain|regex_escape }}$'
   url: {{ matrix_mautrix_facebook_appservice_address }}
   # See https://github.com/tulir/mautrix-signal/issues/43
-  sender_localpart: _bot_{{ matrix_mautrix_facebook_appservice_bot_username|to_json }}
+  sender_localpart: _bot_{{ matrix_mautrix_facebook_appservice_bot_username }}
   rate_limited: false
 
 matrix_mautrix_facebook_registration: "{{ matrix_mautrix_facebook_registration_yaml|from_yaml }}"

roles/matrix-bridge-mautrix-signal/templates/registration.yaml.j2

@@ -13,5 +13,5 @@ namespaces:
       regex: '^#signal_.+:{{ matrix_mautrix_signal_homeserver_domain|regex_escape }}$'
 url: {{ matrix_mautrix_signal_appservice_address }}
 # See https://github.com/tulir/mautrix-signal/issues/43
-sender_localpart: _bot_{{ matrix_mautrix_signal_appservice_bot_username|to_json }}
+sender_localpart: _bot_{{ matrix_mautrix_signal_appservice_bot_username }}
 rate_limited: false

roles/matrix-bridge-mautrix-telegram/defaults/main.yml

@@ -117,7 +117,7 @@ matrix_mautrix_telegram_registration_yaml: |
       - exclusive: true
         regex: '^#telegram_.+:{{ matrix_mautrix_telegram_homeserver_domain|regex_escape }}$'
   # See https://github.com/tulir/mautrix-signal/issues/43
-  sender_localpart: _bot_{{ matrix_mautrix_telegram_appservice_bot_username|to_json }}
+  sender_localpart: _bot_{{ matrix_mautrix_telegram_appservice_bot_username }}
   sender_localpart: telegrambot
   rate_limited: false
 

roles/matrix-bridge-mautrix-whatsapp/defaults/main.yml

@@ -96,7 +96,7 @@ matrix_mautrix_whatsapp_registration_yaml: |
   as_token: "{{ matrix_mautrix_whatsapp_appservice_token }}"
   hs_token: "{{ matrix_mautrix_whatsapp_homeserver_token }}"
   # See https://github.com/tulir/mautrix-signal/issues/43
-  sender_localpart: _bot_{{ matrix_mautrix_whatsapp_appservice_bot_username|to_json }}
+  sender_localpart: _bot_{{ matrix_mautrix_whatsapp_appservice_bot_username }}
   rate_limited: false
   namespaces:
       users: