Rename get_e2e_device_keys to better reflect its purpose (#8205)

... and to show that it does something slightly different to
`_get_e2e_device_keys_txn`.

`include_all_devices` and `include_deleted_devices` were never used (and
`include_deleted_devices` was broken, since that would cause `None`s in the
result which were not handled in the loop below.

Add some typing too.

synapse/handlers/e2e_keys.py

@@ -353,7 +353,7 @@ class E2eKeysHandler(object):
             # make sure that each queried user appears in the result dict
             result_dict[user_id] = {}
 
-        results = await self.store.get_e2e_device_keys(local_query)
+        results = await self.store.get_e2e_device_keys_for_cs_api(local_query)
 
         # Build the result structure
         for user_id, device_keys in results.items():
@@ -734,7 +734,7 @@ class E2eKeysHandler(object):
             # fetch our stored devices.  This is used to 1. verify
             # signatures on the master key, and 2. to compare with what
             # was sent if the device was signed
-            devices = await self.store.get_e2e_device_keys([(user_id, None)])
+            devices = await self.store.get_e2e_device_keys_for_cs_api([(user_id, None)])
 
             if user_id not in devices:
                 raise NotFoundError("No device keys found")