[M116] In VideoCaptureDS::{Start|Stop}Capture do not lock

Sequence- and RaceCheckers ensure thread safety, and show that these
locks protect nothing.

(cherry picked from commit dcf600d)

Bug: webrtc:15181, chromium:1457919
Change-Id: I7c26cd9aea5fa72ad9435de5ec1b9135ac22b1e8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/305649
Reviewed-by: Ilya Nikolaevskiy <[email protected]>
Commit-Queue: Ilya Nikolaevskiy <[email protected]>
Reviewed-by: Per Kjellander <[email protected]>
Cr-Original-Commit-Position: refs/heads/main@{#40345}
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/310520
Reviewed-by: Henrik Boström <[email protected]>
Cr-Commit-Position: refs/branch-heads/5845@{#3}
Cr-Branched-From: f80cf81-refs/heads/main@{#40319}

Author: Pehrsons

modules/video_capture/windows/video_capture_ds.cc

@@ -125,7 +125,6 @@ int32_t VideoCaptureDS::Init(const char* deviceUniqueIdUTF8) {
 
 int32_t VideoCaptureDS::StartCapture(const VideoCaptureCapability& capability) {
   RTC_DCHECK_RUN_ON(&api_checker_);
-  MutexLock lock(&api_lock_);
 
   if (capability != _requestedCapability) {
     DisconnectGraph();
@@ -150,7 +149,6 @@ int32_t VideoCaptureDS::StartCapture(const VideoCaptureCapability& capability) {
 
 int32_t VideoCaptureDS::StopCapture() {
   RTC_DCHECK_RUN_ON(&api_checker_);
-  MutexLock lock(&api_lock_);
 
   HRESULT hr = _mediaControl->StopWhenReady();
   if (FAILED(hr)) {