The lock isn't really needed as encoder_queue_is_active_ can be checked
on the task queue to provide synchronization.
There is one behavioral change due to this: We will not cancel any currently
pending encoding tasks when we stop sending, they will be allowed to finish.
Bug: webrtc:10365
Change-Id: I2b4897dde8d49bc7ee5d2d69694616aee8aaea38
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/125096
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26963}
9b9344742b