Remove ALL usage of CriticalSectionWrapper.

Finally we are able to remove this class entirely, along with the last
vestiges of it's use. I've also removed some legacy files that were only
used for windows XP support.

BUG=webrtc:7035

Review-Url: https://codereview.webrtc.org/2790533002
Cr-Commit-Position: refs/heads/master@{#17480}

webrtc/modules/video_coding/jitter_buffer.h

@@ -18,6 +18,7 @@
 #include <vector>
 
 #include "webrtc/base/constructormagic.h"
+#include "webrtc/base/criticalsection.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/modules/utility/include/process_thread.h"
@@ -28,7 +29,6 @@
 #include "webrtc/modules/video_coding/jitter_buffer_common.h"
 #include "webrtc/modules/video_coding/jitter_estimator.h"
 #include "webrtc/modules/video_coding/nack_module.h"
-#include "webrtc/system_wrappers/include/critical_section_wrapper.h"
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
@@ -315,7 +315,7 @@ class VCMJitterBuffer {
   Clock* clock_;
   // If we are running (have started) or not.
   bool running_;
-  CriticalSectionWrapper* crit_sect_;
+  rtc::CriticalSection crit_sect_;
   // Event to signal when we have a frame ready for decoder.
   std::unique_ptr<EventWrapper> frame_event_;
   // Number of allocated frames.