How to remove WP Title Tag?

The default <title> can be handled by a template as a direct input in header.php or by the theme setup or options screen in backend.

If your theme won’t show up <title> tag in the header.php, then it’s pretty likely than the functions.php file has something like this:

add_theme_support( 'title-tag' );

You can remove that line and it won’t print the title tag in head, so you can do it manually.