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/remote_bitrate_estimator/BUILD.gn b/modules/remote_bitrate_estimator/BUILD.gn
index 31eb46c..b157f3d 100644
--- a/modules/remote_bitrate_estimator/BUILD.gn
+++ b/modules/remote_bitrate_estimator/BUILD.gn
@@ -46,7 +46,6 @@
   deps = [
     "../..:webrtc_common",
     "../../:typedefs",
-    "../../api:optional",
     "../../modules:module_api",
     "../../modules/rtp_rtcp:rtp_rtcp_format",
     "../../rtc_base:checks",
@@ -55,6 +54,7 @@
     "../../system_wrappers",
     "../../system_wrappers:field_trial_api",
     "../../system_wrappers:metrics_api",
+    "//third_party/abseil-cpp/absl/types:optional",
   ]
 }
 
@@ -135,7 +135,6 @@
       "..:module_api",
       "../..:webrtc_common",
       "../../:typedefs",
-      "../../api:optional",
       "../../logging:mocks",
       "../../rtc_base:checks",
       "../../rtc_base:gtest_prod",
@@ -161,6 +160,7 @@
       "../rtp_rtcp:rtp_rtcp_format",
       "../video_coding:video_coding_utility",
       "//testing/gtest",
+      "//third_party/abseil-cpp/absl/types:optional",
     ]
   }