Remove references to MatrixClient.crypto (#28204)

* Remove `VerificationExplorer`

* Remove `remakeolm` slash command

* Remove call to `crypto.cancelAndResendAllOutgoingKeyRequests`

* Remove crypto mock in `LoginWithQR-test.tsx`

* Remove `StopGadWidgetDriver.sendToDevice`

* Remove remaining mock

test/test-utils/test-utils.ts

@@ -119,11 +119,6 @@ export function createTestClient(): MatrixClient {
             removeRoom: jest.fn(),
         },
 
-        crypto: {
-            deviceList: {
-                downloadKeys: jest.fn(),
-            },
-        },
         getCrypto: jest.fn().mockReturnValue({
             getOwnDeviceKeys: jest.fn(),
             getUserDeviceInfo: jest.fn(),