Use the correct action hook
Notice the action hook being used:
add_action( 'wp_enqueue_scripts', 'add_our_scripts',0);
And the action hook you’re defining/using:
add_action( 'test_remove_scripts', 'remove_radium_scripts', 999 );
You need to hook into the same action:
add_action( 'wp_enqueue_scripts', 'remove_radium_scripts', 999 );
Use the correct priority
Notice the priority being used:
add_action( 'wp_enqueue_scripts', 'add_our_scripts',0);
And the priority you’re using:
add_action( 'wp_enqueue_scripts', 'remove_radium_scripts', 999 );
You need to hook into the same priority:
add_action( 'wp_enqueue_scripts', 'remove_radium_scripts', 0 );
If all else fails, use last-minute dequeue
If those don’t work, you can use a more aggressive option: dequeue at wp_print_styles, with a high priority:
add_action( 'wp_print_styles', 'remove_radium_scripts', 9999 );