Remove the emergency alerts canary

See https://github.com/alphagov/notifications-broadcasts-infra/pull/197
for why we no longer need this and we get to delete some code!

app/clients/cbc_proxy.py

@@ -48,7 +48,6 @@ class CBCProxyClient:
 
     def get_proxy(self, provider):
         proxy_classes = {
-            'canary': CBCProxyCanary,
             BroadcastProvider.EE: CBCProxyEE,
             BroadcastProvider.THREE: CBCProxyThree,
             BroadcastProvider.O2: CBCProxyO2,
@@ -81,12 +80,6 @@ class CBCProxyClientBase(ABC):
     def __init__(self, lambda_client):
         self._lambda_client = lambda_client
 
-    def send_canary(
-        self,
-        identifier,
-    ):
-        pass
-
     def send_link_test(
         self,
         identifier,
@@ -162,26 +155,6 @@ class CBCProxyClientBase(ABC):
         return self.LANGUAGE_ENGLISH
 
 
-class CBCProxyCanary(CBCProxyClientBase):
-    """
-    The canary is a lambda which tests notify's connectivity to the Cell Broadcast AWS infrastructure. It calls the
-    canary, a specific lambda that does not open a vpn or connect to a provider but just responds from within AWS.
-    """
-    lambda_name = 'canary'
-    # we don't need a failover lambda for the canary as it doesn't actually make calls out to a CBC
-    # so we just reuse the normal one in case of a failover scenario
-    failover_lambda_name = 'canary'
-
-    LANGUAGE_ENGLISH = None
-    LANGUAGE_WELSH = None
-
-    def send_canary(
-        self,
-        identifier,
-    ):
-        self._invoke_lambda(self.lambda_name, payload={'identifier': identifier})
-
-
 class CBCProxyOne2ManyClient(CBCProxyClientBase):
     LANGUAGE_ENGLISH = 'en-GB'
     LANGUAGE_WELSH = 'cy-GB'