Delete obsolete email DCHECK in local card migration dialog view

This DCHECK makes sure the email passed in CreateExplanationText() is
not empty, but we later made change so that this function will be called
when creating feedback dialog view where there is no user email address.

So this DCHECK will always fail on an expected event.

Bug: 897998
Change-Id: Id22300ba56fcc4de15f014a554d5c2d1e88df01d
Reviewed-on: https://chromium-review.googlesource.com/c/1474805
Commit-Queue: Siyu An <siyua@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632800}

chrome/browser/ui/views/autofill/local_card_migration_dialog_view.cc

@@ -98,12 +98,12 @@ std::unique_ptr<views::Label> CreateExplanationText(
     LocalCardMigrationDialogState view_state,
     int card_list_size,
     const base::string16& user_email) {
-  DCHECK_NE((int)user_email.length(), 0);
   auto explanation_text =
       std::make_unique<views::Label>(base::string16(), CONTEXT_BODY_TEXT_LARGE,
                                      ChromeTextStyle::STYLE_SECONDARY);
   switch (view_state) {
     case LocalCardMigrationDialogState::kOffered:
+      DCHECK(!user_email.empty());
       explanation_text->SetText(
           base::i18n::MessageFormatter::FormatWithNumberedArgs(
               l10n_util::GetStringFUTF16(