Delete some unneeded code in the ElementCall class (#32879)

* Remove redundant call intent computation

I'm not clear on why we've been computing the intent of a call twice — first in generateWidgetUrl and then again in getWidgetData. Adding intent to the widget's data has no effect at all since there is no matching placeholder in the URL for it to be templated into. It seems we can safely delete this code.

* Remove preload hack

Element Web has long since upgraded past version 0.15.0 of Element Call, so we no longer need to set the preload parameter manually.

apps/web/playwright/e2e/voip/element-call.spec.ts

@@ -37,7 +37,6 @@ function assertCommonCallParameters(
     expect(hash.get("userId")).toEqual(user.userId);
     expect(hash.get("deviceId")).toEqual(user.deviceId);
     expect(hash.get("roomId")).toEqual(room.roomId);
-    expect(hash.get("preload")).toEqual("false");
 }
 
 async function sendRTCState(bot: Bot, roomId: string, notification?: "ring" | "notification", intent?: string) {