Remove unused sessionStorage layer (#8834)

* Remove unused sessionStorage layer

* Update global.d.ts

* Fix tests

cypress/support/bot.ts

@@ -20,7 +20,6 @@ import request from "browser-request";
 
 import type { MatrixClient } from "matrix-js-sdk/src/client";
 import { SynapseInstance } from "../plugins/synapsedocker";
-import { MockStorage } from "./storage";
 import Chainable = Cypress.Chainable;
 
 declare global {
@@ -51,7 +50,6 @@ Cypress.Commands.add("getBot", (synapse: SynapseInstance, displayName?: string):
                 store: new win.matrixcs.MemoryStore(),
                 scheduler: new win.matrixcs.MatrixScheduler(),
                 cryptoStore: new win.matrixcs.MemoryCryptoStore(),
-                sessionStore: new win.matrixcs.WebStorageSessionStore(new MockStorage()),
             });
 
             cli.on(win.matrixcs.RoomMemberEvent.Membership, (event, member) => {