Revert "[iOS] Restore the user agent only on iOS 13+"

This reverts commit 21eb2224.

Reason for revert: Causing failures on ios_web_unittests on iOS12

https://ci.chromium.org/p/chrome/builders/ci/iphone-device/7949

Original change's description:
> [iOS] Restore the user agent only on iOS 13+
> 
> This CL restrict the user agent restoration to iOS 13 and further as
> iOS 12 has an issue getting the right User Agent.
> 
> Bug: 1070593
> Change-Id: Ie4570efcb9931ccb8662511b16a1298570f0a297
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2154189
> Reviewed-by: Justin Cohen <justincohen@chromium.org>
> Commit-Queue: Gauthier Ambard <gambard@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#760057}

TBR=justincohen@chromium.org,gambard@chromium.org

Change-Id: I0458f2cea4df855599dd8fa72692b7ff4840ef06
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1070593
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2153733Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760192}

ios/web/navigation/wk_based_navigation_manager_impl.mm

@@ -741,16 +741,12 @@ void WKBasedNavigationManagerImpl::UnsafeRestore(
     forward_items.push_back(std::move(items[index]));
   }
 
-  if (@available(iOS 13, *)) {
-    AddRestoreCompletionCallback(
-        base::BindOnce(&WKBasedNavigationManagerImpl::RestoreItemsState,
-                       base::Unretained(this), RestoreItemListType::kBackList,
-                       std::move(back_items)));
-    AddRestoreCompletionCallback(base::BindOnce(
-        &WKBasedNavigationManagerImpl::RestoreItemsState,
-        base::Unretained(this), RestoreItemListType::kForwardList,
-        std::move(forward_items)));
-  }
+  AddRestoreCompletionCallback(base::BindOnce(
+      &WKBasedNavigationManagerImpl::RestoreItemsState, base::Unretained(this),
+      RestoreItemListType::kBackList, std::move(back_items)));
+  AddRestoreCompletionCallback(base::BindOnce(
+      &WKBasedNavigationManagerImpl::RestoreItemsState, base::Unretained(this),
+      RestoreItemListType::kForwardList, std::move(forward_items)));
 
   LoadURLWithParams(params);
 
@@ -799,10 +795,8 @@ void WKBasedNavigationManagerImpl::RestoreItemsState(
 void WKBasedNavigationManagerImpl::RestoreVisibleItemState() {
   NavigationItemImpl* last_committed_item =
       GetLastCommittedItemInCurrentOrRestoredSession();
-  if (@available(iOS 13, *)) {
-    if (restored_visible_item_ && last_committed_item) {
-      last_committed_item->RestoreStateFromItem(restored_visible_item_.get());
-    }
+  if (restored_visible_item_ && last_committed_item) {
+    last_committed_item->RestoreStateFromItem(restored_visible_item_.get());
   }
   restored_visible_item_.reset();
 }