Replace some custom React hooks with observable-hooks (#2710)

The observable-hooks package provides hooks that do exactly the same thing as these custom React hooks I had written a while back. (even the names are the same, wow)

Co-authored-by: Hugh Nimmo-Smith <hughns@element.io>

src/state/useObservable.ts

@@ -1,34 +0,0 @@
-/*
-Copyright 2023, 2024 New Vector Ltd.
-
-SPDX-License-Identifier: AGPL-3.0-only
-Please see LICENSE in the repository root for full details.
-*/
-
-import { Ref, useCallback, useRef } from "react";
-import { BehaviorSubject, Observable } from "rxjs";
-
-import { useInitial } from "../useInitial";
-
-/**
- * React hook that creates an Observable from a changing value. The Observable
- * replays its current value upon subscription and emits whenever the value
- * changes.
- */
-export function useObservable<T>(value: T): Observable<T> {
-  const subject = useRef<BehaviorSubject<T>>();
-  subject.current ??= new BehaviorSubject(value);
-  if (value !== subject.current.value) subject.current.next(value);
-  return subject.current;
-}
-
-/**
- * React hook that creates a ref and an Observable that emits any values
- * stored in the ref. The Observable replays the value currently stored in the
- * ref upon subscription.
- */
-export function useObservableRef<T>(initialValue: T): [Observable<T>, Ref<T>] {
-  const subject = useInitial(() => new BehaviorSubject(initialValue));
-  const ref = useCallback((value: T) => subject.next(value), [subject]);
-  return [subject, ref];
-}