Using Theme Customizer Built-In Sections

The default controls are registered in WP_Customize_Manager::register_controls(), which is hooked to customize_register. This action is fired in another method, wp_loaded(), which is hooked to the action of the same name.

To remove these default controls, use your own handler on customize_register with a later priority, so that it runs after register_controls() has added them:

function wpse_185386_remove_customize_controls( $wp_customize ) {
    $wp_customize->remove_section( 'title_tagline' );
}

add_action( 'customize_register', 'wpse_185386_remove_customize_controls', 50 /* Priority */ );