Remove unused includes from {byte,wide}string.h

Many of these includes are no longer needed, as their uses moved into
string_template.h.

Change-Id: I61ca7f58609c9c9caf89965a0a3c9555f4319099
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/119370
Reviewed-by: Thomas Sepez <tsepez@google.com>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
diff --git a/core/fxcrt/bytestring.h b/core/fxcrt/bytestring.h
index d8fb28d..498b454 100644
--- a/core/fxcrt/bytestring.h
+++ b/core/fxcrt/bytestring.h
@@ -11,19 +11,11 @@
 #include <stddef.h>
 #include <stdint.h>
 
-#include <functional>
 #include <iosfwd>
-#include <iterator>
-#include <optional>
 #include <utility>
 
-#include "core/fxcrt/check.h"
 #include "core/fxcrt/fx_string_wrappers.h"
-#include "core/fxcrt/retain_ptr.h"
-#include "core/fxcrt/span.h"
-#include "core/fxcrt/string_data_template.h"
 #include "core/fxcrt/string_template.h"
-#include "core/fxcrt/string_view_template.h"
 
 namespace fxcrt {
 
diff --git a/core/fxcrt/widestring.h b/core/fxcrt/widestring.h
index 4fabdea..38be8ea 100644
--- a/core/fxcrt/widestring.h
+++ b/core/fxcrt/widestring.h
@@ -11,18 +11,11 @@
 #include <stddef.h>
 #include <stdint.h>
 
-#include <functional>
 #include <iosfwd>
-#include <iterator>
-#include <optional>
 #include <utility>
 
-#include "core/fxcrt/check.h"
-#include "core/fxcrt/retain_ptr.h"
 #include "core/fxcrt/span.h"
-#include "core/fxcrt/string_data_template.h"
 #include "core/fxcrt/string_template.h"
-#include "core/fxcrt/string_view_template.h"
 
 namespace fxcrt {