Remove unused variable in autofill_private_api

This patch means removing variable unused.
string16Container looks like used in legacy code.

Bug: None
Change-Id: I17867cd8c48dd13c1fb46c3376d5424f5ccacf3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1828665Reviewed-by: sebsg <sebsg@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Jaeyong Bae <jdragon.bae@gmail.com>
Cr-Commit-Position: refs/heads/master@{#702473}

chrome/browser/extensions/api/autofill_private/autofill_private_api.cc

@@ -124,10 +124,6 @@ ExtensionFunction::ResponseAction AutofillPrivateSaveAddressFunction::Run() {
           ? *existing_profile
           : autofill::AutofillProfile(base::GenerateGUID(), kSettingsOrigin);
 
-  // Strings from JavaScript use UTF-8 encoding. This container is used as an
-  // intermediate container for functions which require UTF-16 strings.
-  std::vector<base::string16> string16Container;
-
   if (address->full_names) {
     std::string full_name;
     if (!address->full_names->empty())