Replace rtc::Optional with absl::optional in audio, call and video

This is a no-op change because rtc::Optional is an alias to absl::optional

This CL generated by running script with parameters 'audio call video':
#!/bin/bash
find $@ -type f \( -name \*.h -o -name \*.cc \) \
-exec sed -i 's|rtc::Optional|absl::optional|g' {} \+ \
-exec sed -i 's|rtc::nullopt|absl::nullopt|g' {} \+ \
-exec sed -i 's|#include "api/optional.h"|#include "absl/types/optional.h"|' {} \+

find $@ -type f -name BUILD.gn \
-exec sed -r -i 's|"(../)*api:optional"|"//third_party/abseil-cpp/absl/types:optional"|' {} \+;

git cl format

Bug: webrtc:9078
Change-Id: I02c5db956846a88a268a300ba086703a02d62e36
Reviewed-on: https://webrtc-review.googlesource.com/83722
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23628}
diff --git a/video/BUILD.gn b/video/BUILD.gn
index f56a71d..df50d90 100644
--- a/video/BUILD.gn
+++ b/video/BUILD.gn
@@ -62,7 +62,6 @@
     "../:typedefs",
     "../api:fec_controller_api",
     "../api:libjingle_peerconnection_api",
-    "../api:optional",
     "../api:transport_api",
     "../api/video:video_frame",
     "../api/video:video_frame_i420",
@@ -84,6 +83,7 @@
     "../rtc_base/system:fallthrough",
     "../system_wrappers:field_trial_api",
     "../system_wrappers:metrics_api",
+    "//third_party/abseil-cpp/absl/types:optional",
 
     # For RtxReceiveStream.
     "../call:rtp_receiver",
@@ -121,7 +121,6 @@
   ]
 
   deps = [
-    "../api:optional",
     "../api/video:encoded_frame",
     "../api/video:video_frame",
     "../api/video:video_stream_decoder",
@@ -130,6 +129,7 @@
     "../rtc_base:rtc_base_approved",
     "../rtc_base:rtc_task_queue_api",
     "../system_wrappers:system_wrappers",
+    "//third_party/abseil-cpp/absl/types:optional",
   ]
 }
 
@@ -364,7 +364,6 @@
     deps = [
       ":video",
       ":video_mocks",
-      "../api:optional",
       "../api/video:video_frame",
       "../api/video:video_frame_i420",
       "../api/video_codecs:video_codecs_api",
@@ -417,6 +416,7 @@
       "../test:test_support",
       "../test:video_test_common",
       "//testing/gtest",
+      "//third_party/abseil-cpp/absl/types:optional",
     ]
     if (!build_with_chromium && is_clang) {
       # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).