Second batch: remove deprecated calls on MatrixClient (#28227)

* Replace `MatrixClient.forceDiscardSession` call by `MatrixClient.CryptoApi.forceDiscardSession`

* Remove `MatrixClient.scheduleAllGroupSessionsForBackup` mock

test/test-utils/test-utils.ts

@@ -166,7 +166,6 @@ export function createTestClient(): MatrixClient {
             });
         }),
         mxcUrlToHttp: jest.fn().mockImplementation((mxc: string) => `http://this.is.a.url/${mxc.substring(6)}`),
-        scheduleAllGroupSessionsForBackup: jest.fn().mockResolvedValue(undefined),
         setAccountData: jest.fn(),
         setRoomAccountData: jest.fn(),
         setRoomTopic: jest.fn(),