Delete unused.h include from api as unused

Bug: None
Change-Id: Ib62bdc296fdff8ecb3eb5b22d5eda1ef8fc35284
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/202036
Reviewed-by: Christoffer Rodbro <crodbro@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33026}

api/voip/BUILD.gn

@@ -21,7 +21,6 @@ rtc_source_set("voip_api") {
   ]
   deps = [
     "..:array_view",
-    "../../rtc_base/system:unused",
     "../audio_codecs:audio_codecs_api",
     "../neteq:neteq_api",
   ]

api/voip/DEPS

@@ -3,10 +3,6 @@ specific_include_rules = {
     "+third_party/absl/types/optional.h",
   ],
 
-  "voip_base.h": [
-    "+rtc_base/system/unused.h",
-  ],
-
   "voip_engine_factory.h": [
     "+modules/audio_device/include/audio_device.h",
     "+modules/audio_processing/include/audio_processing.h",

api/voip/voip_base.h

@@ -13,7 +13,6 @@
 
 #include "absl/base/attributes.h"
 #include "absl/types/optional.h"
-#include "rtc_base/system/unused.h"
 
 namespace webrtc {