Avoid a packetstorm of device queries on startup

Two main changes here:
 * when we get an m.new_device event for a device we know about, ignore it
 * Batch up the m.new_device events received during initialsync and spam out
   all the queries at once.

lib/crypto/algorithms/base.js

@@ -88,15 +88,6 @@ EncryptionAlgorithm.prototype.onRoomMembership = function(
     event, member, oldMembership
 ) {};
 
-/**
- * Called when a new device announces itself in the room
- *
- * @param {string} userId    owner of the device
- * @param {string} deviceId  deviceId of the device
- */
-EncryptionAlgorithm.prototype.onNewDevice = function(userId, deviceId) {};
-
-
 /**
  * base type for decryption implementations
  *