Unwrap removeIdentityKey from calls to saveIdentity

saveIdentity is now reponsible for determining firstUse, so we must not remove
the existing key before updating it.

Previously, the implementation provided an extra check against overwritting an
existing key, but that should be done via isTrustedIdentity instead.

// FREEBIE

js/models/conversations.js

@@ -504,7 +504,6 @@
             throw 'No conflicts to resolve';
         }
 
-        return textsecure.storage.protocol.removeIdentityKey(number).then(function() {
         return textsecure.storage.protocol.saveIdentity(number, identityKey).then(function() {
             var promise = Promise.resolve();
             var conflicts = this.messageCollection.filter(function(message) {
@@ -524,7 +523,6 @@
             });
             return promise;
         }.bind(this));
-        }.bind(this));
     },
     notify: function(message) {
         if (!message.isIncoming()) {

js/signal_protocol_store.js

@@ -293,13 +293,11 @@
                     if (!oldpublicKey || equalArrayBuffers(oldpublicKey, publicKey)) {
                         resolve(true);
                     } else if (!storage.get('safety-numbers-approval', true)) {
-                        this.removeIdentityKey(identifier).then(function() {
                         this.saveIdentity(identifier, publicKey).then(function() {
                             console.log('Key changed for', identifier);
                             this.trigger('keychange', identifier);
                             resolve(true);
                         }.bind(this));
-                        }.bind(this));
                     } else {
                         resolve(false);
                     }