Remove unused critical section includes.

Bug: webrtc:11567
Change-Id: Ic5e43c51ce06c0619adc265d12ad4bef73a9df76
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/179521
Reviewed-by: Tommi <tommi@webrtc.org>
Commit-Queue: Markus Handell <handellm@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31745}
diff --git a/rtc_base/system/file_wrapper.h b/rtc_base/system/file_wrapper.h
index 24c333a..42c463c 100644
--- a/rtc_base/system/file_wrapper.h
+++ b/rtc_base/system/file_wrapper.h
@@ -14,7 +14,7 @@
 #include <stddef.h>
 #include <stdio.h>
 
-#include "rtc_base/critical_section.h"
+#include <string>
 
 // Implementation that can read (exclusive) or write from/to a file.