[cr149] TemplateURLTableModel::RowCount deleted

A new member `engine_count()` serves the same purpose.

Chromium changes:
https://chromium.googlesource.com/chromium/src/+/0bd93729174039f678c71990a698215207d985b5

commit 0bd93729174039f678c71990a698215207d985b5
Author: Amelie Schneider <amelies@google.com>
Date:   Thu Apr 23 08:29:23 2026 -0700

    [Search] Remove unused TemplateURLTableModel functions

    The experiment `SearchSettingsUpdate` included a refactoring to stop
    using the table model for accessing the template URL service but
    accessing it directly through the keyword controller instead. Some
    functions are already unused and can be removed, the
    TemplateURLTableModel as a whole should be removed once the flag is
    launched.

    This also excludes KeywordEditorController for Android, since it is not
    used there.

    Bug: 498543733, 490316630
    Change-Id: Ie7ab74e7eece7485c85a678b89a48f1cb15a9a94
    Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7768616
    Reviewed-by: Nicolas Dossou-Gbété <dgn@chromium.org>
    Commit-Queue: Amelie Schneider <amelies@google.com>
    Cr-Commit-Position: refs/heads/main@{#1619543}

browser/ui/webui/settings/brave_search_engines_handler.cc

@@ -139,7 +139,7 @@ void BraveSearchEnginesHandler::HandleSetDefaultPrivateSearchEngine(
   CHECK_EQ(1U, args.size());
   int index = args[0].GetInt();
   if (index < 0 || static_cast<size_t>(index) >=
-                       list_controller_.table_model()->RowCount()) {
+                       list_controller_.table_model()->engine_count()) {
     return;
   }