Replace rtc::Optional with absl::optional in media, ortc, p2p

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

This CL generated by running script with parameters 'media ortc p2p':
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: I19167714af7cc1436d34cfcba6c8b3718d8e677b
Reviewed-on: https://webrtc-review.googlesource.com/83731
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23638}
diff --git a/p2p/BUILD.gn b/p2p/BUILD.gn
index 07d1f71..55e96ca 100644
--- a/p2p/BUILD.gn
+++ b/p2p/BUILD.gn
@@ -83,7 +83,6 @@
 
   deps = [
     "../api:libjingle_peerconnection_api",
-    "../api:optional",
     "../api:ortc_api",
     "../logging:ice_log",
     "../rtc_base:checks",
@@ -91,6 +90,7 @@
     "../rtc_base:safe_minmax",
     "../rtc_base:stringutils",
     "../system_wrappers:field_trial_api",
+    "//third_party/abseil-cpp/absl/types:optional",
   ]
 
   if (build_with_chromium) {