Remove third_party/base/optional.h.

Replace with absl everywhere.

Bug: pdfium:1726
Change-Id: I08118cd765626a0703a0692c812872915594c370
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/85519
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
diff --git a/fxjs/cjs_field.cpp b/fxjs/cjs_field.cpp
index ba447b1..3ffae49 100644
--- a/fxjs/cjs_field.cpp
+++ b/fxjs/cjs_field.cpp
@@ -27,9 +27,9 @@
 #include "fxjs/cjs_icon.h"
 #include "fxjs/fxv8.h"
 #include "fxjs/js_resources.h"
+#include "third_party/abseil-cpp/absl/types/optional.h"
 #include "third_party/base/check.h"
 #include "third_party/base/notreached.h"
-#include "third_party/base/optional.h"
 #include "v8/include/v8-container.h"
 
 namespace {