Reland "[cleanup] Remove useless includes."

Reason for reland: Downstream project fixed.

Original change's description:

> [cleanup] Remove useless includes.
>
> Manual cleanup guided by include-what-you-use diagnostic.
>
> Bug: webrtc:8311
> Change-Id: I00be03392cc7ee005101427ea7dc701621ccea68
> Reviewed-on: https://webrtc-review.googlesource.com/c/103320
> Commit-Queue: Yves Gerey <yvesg@webrtc.org>
> Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#25013}

Bug: webrtc:8311
Change-Id: Id6ec4aeb798886a90ace640a190eaf16497ba31b
Reviewed-on: https://webrtc-review.googlesource.com/c/104120
Commit-Queue: Yves Gerey <yvesg@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25034}
diff --git a/rtc_base/task_queue_libevent.cc b/rtc_base/task_queue_libevent.cc
index d3b1a7c..ce05bae 100644
--- a/rtc_base/task_queue_libevent.cc
+++ b/rtc_base/task_queue_libevent.cc
@@ -10,11 +10,17 @@
 
 #include "rtc_base/task_queue.h"
 
+#include <errno.h>  // for EAGAIN, errno
 #include <fcntl.h>
+#include <pthread.h>  // for pthread_getspecific
 #include <signal.h>
-#include <string.h>
+#include <stdint.h>  // for uint32_t
+#include <time.h>    // for nanosleep, timespec
 #include <unistd.h>
 #include <list>
+#include <memory>       // for unique_ptr, allocator
+#include <type_traits>  // for remove_reference<>::...
+#include <utility>      // for move
 
 #include "base/third_party/libevent/event.h"
 #include "rtc_base/checks.h"
@@ -22,11 +28,13 @@
 #include "rtc_base/logging.h"
 #include "rtc_base/numerics/safe_conversions.h"
 #include "rtc_base/platform_thread.h"
+#include "rtc_base/platform_thread_types.h"  // for CurrentThreadRef
 #include "rtc_base/refcount.h"
 #include "rtc_base/refcountedobject.h"
+#include "rtc_base/scoped_ref_ptr.h"  // for scoped_refptr
 #include "rtc_base/system/unused.h"
-#include "rtc_base/task_queue.h"
 #include "rtc_base/task_queue_posix.h"
+#include "rtc_base/thread_annotations.h"  // for RTC_GUARDED_BY
 #include "rtc_base/timeutils.h"
 
 namespace rtc {