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/rtp_streams_synchronizer.cc b/video/rtp_streams_synchronizer.cc
index c330a44..cc7f893 100644
--- a/video/rtp_streams_synchronizer.cc
+++ b/video/rtp_streams_synchronizer.cc
@@ -76,13 +76,13 @@
   }
   RTC_DCHECK(sync_.get());
 
-  rtc::Optional<Syncable::Info> audio_info = syncable_audio_->GetInfo();
+  absl::optional<Syncable::Info> audio_info = syncable_audio_->GetInfo();
   if (!audio_info || !UpdateMeasurements(&audio_measurement_, *audio_info)) {
     return;
   }
 
   int64_t last_video_receive_ms = video_measurement_.latest_receive_time_ms;
-  rtc::Optional<Syncable::Info> video_info = syncable_video_->GetInfo();
+  absl::optional<Syncable::Info> video_info = syncable_video_->GetInfo();
   if (!video_info || !UpdateMeasurements(&video_measurement_, *video_info)) {
     return;
   }