Replace rtc::Optional with absl::optional

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

This CL generated by running script from modules with parameters
'pacing video_coding congestion_controller remote_bitrate_estimator':

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: I8ea501d7f1ee36e8d8cd3ed37e6b763c7fe29118
Reviewed-on: https://webrtc-review.googlesource.com/83900
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23640}
diff --git a/modules/congestion_controller/goog_cc/probe_controller.cc b/modules/congestion_controller/goog_cc/probe_controller.cc
index c05c094..fbc0620 100644
--- a/modules/congestion_controller/goog_cc/probe_controller.cc
+++ b/modules/congestion_controller/goog_cc/probe_controller.cc
@@ -209,7 +209,7 @@
 }
 
 void ProbeController::SetAlrStartTimeMs(
-    rtc::Optional<int64_t> alr_start_time_ms) {
+    absl::optional<int64_t> alr_start_time_ms) {
   alr_start_time_ms_ = alr_start_time_ms;
 }
 void ProbeController::SetAlrEndedTimeMs(int64_t alr_end_time_ms) {