Fix deadlock in TaskQueueGcd::Delete() when called from the queue.

On return from Delete(), it is guaranteed that no task is running and
no new tasks are able to start on the task queue.
However, if Delete() is called from a task running on that same queue,
dispatch_sync will deadlock.

This CL allows Delete() to be called from the current queue by
skipping the dispatch_sync and setting is_active_ to false directly.
GCD's reference counting ensures that the queue is not deallocated
until the current task finishes.

Bug: b/492945633
Change-Id: I75ca201273613c47f58c4ccf218af915832ed597
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/464460
Commit-Queue: Tony Herre <herre@google.com>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47439}