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/call/callfactory.cc b/call/callfactory.cc
index 4ab5b89..b5c28d2 100644
--- a/call/callfactory.cc
+++ b/call/callfactory.cc
@@ -14,7 +14,7 @@
 #include <string>
 #include <utility>
 
-#include "api/optional.h"
+#include "absl/types/optional.h"
 #include "call/call.h"
 #include "call/degraded_call.h"
 #include "call/fake_network_pipe.h"
@@ -30,7 +30,7 @@
   return (sscanf(group.c_str(), "%d", field) == 1);
 }
 
-rtc::Optional<webrtc::FakeNetworkPipe::Config> ParseDegradationConfig(
+absl::optional<webrtc::FakeNetworkPipe::Config> ParseDegradationConfig(
     bool send) {
   std::string exp_prefix = "WebRTCFakeNetwork";
   if (send) {
@@ -62,15 +62,15 @@
   }
   configured |= ParseConfigParam(exp_prefix + "AvgBurstLossLength",
                                  &config.avg_burst_loss_length);
-  return configured ? rtc::Optional<webrtc::FakeNetworkPipe::Config>(config)
-                    : rtc::nullopt;
+  return configured ? absl::optional<webrtc::FakeNetworkPipe::Config>(config)
+                    : absl::nullopt;
 }
 }  // namespace
 
 Call* CallFactory::CreateCall(const Call::Config& config) {
-  rtc::Optional<webrtc::FakeNetworkPipe::Config> send_degradation_config =
+  absl::optional<webrtc::FakeNetworkPipe::Config> send_degradation_config =
       ParseDegradationConfig(true);
-  rtc::Optional<webrtc::FakeNetworkPipe::Config> receive_degradation_config =
+  absl::optional<webrtc::FakeNetworkPipe::Config> receive_degradation_config =
       ParseDegradationConfig(false);
 
   if (send_degradation_config || receive_degradation_config) {