GF Address Enhanced: Filter USA states to only have the Lower 48 + DC. Add this to a plugin, or functions.php in your theme.

contiguous-usa.php

<?php

/**
 * Filter USA states to only have the Lower 48 + DC
 */
add_filter('gf_address_enhanced_smart_states_script_data', function(array $script_data) : array {
    if (isset($script_data['states']['United States'])) {
        // Alaska, Hawaii, and the Armed Forces codes
        $remove = ['AK', 'HI', 'AA', 'AE', 'AP'];

        // filter out states with unwanted codes
        $contiguous = array_filter($script_data['states']['United States'], function($state) use ($remove) {
            return !in_array($state[0], $remove);
        });

        // reset array keys to a natural sequence before adding back
        $script_data['states']['United States'] = array_values($contiguous);
    }
    return $script_data;
});