Delete unneeded includes of system_wrappers/include/sleep.h

Non-test usage is in modules/audio_device and modules/desktop_capture.

Bug: None
Change-Id: Ie7dd89aa40e6dcfa9e49e1956b87b50fd9f1c227
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/190140
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32484}

modules/audio_coding/BUILD.gn

@@ -1391,7 +1391,6 @@ if (rtc_include_tests) {
       "../../rtc_base:rtc_base_approved",
       "../../rtc_base/synchronization:mutex",
       "../../rtc_base/synchronization:rw_lock_wrapper",
-      "../../system_wrappers",
       "../../test:fileutils",
       "../../test:test_support",
     ]

modules/audio_coding/test/iSACTest.cc

@@ -19,7 +19,6 @@
 #include "api/audio_codecs/isac/audio_encoder_isac_float.h"
 #include "rtc_base/strings/string_builder.h"
 #include "rtc_base/time_utils.h"
-#include "system_wrappers/include/sleep.h"
 #include "test/gmock.h"
 #include "test/gtest.h"
 #include "test/testsupport/file_utils.h"