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/video_coding/h264_sps_pps_tracker.cc b/modules/video_coding/h264_sps_pps_tracker.cc
index e8864e2..2b247c9 100644
--- a/modules/video_coding/h264_sps_pps_tracker.cc
+++ b/modules/video_coding/h264_sps_pps_tracker.cc
@@ -219,9 +219,9 @@
     RTC_LOG(LS_WARNING) << "SPS Nalu header missing";
     return;
   }
-  rtc::Optional<SpsParser::SpsState> parsed_sps = SpsParser::ParseSps(
+  absl::optional<SpsParser::SpsState> parsed_sps = SpsParser::ParseSps(
       sps.data() + kNaluHeaderOffset, sps.size() - kNaluHeaderOffset);
-  rtc::Optional<PpsParser::PpsState> parsed_pps = PpsParser::ParsePps(
+  absl::optional<PpsParser::PpsState> parsed_pps = PpsParser::ParsePps(
       pps.data() + kNaluHeaderOffset, pps.size() - kNaluHeaderOffset);
 
   if (!parsed_sps) {