Remove @ledgerhq/connect-kit-loader for good

This is a code diff titled "Remove @ledgerhq/connect-kit-loader for good" that shows changes to a start() function. The three commented-out calls, addDelegateButton, addBuyButton, and addConnectedComponents, are re-enabled, with their arguments passed as allowlistPromise, delegationsPromise, and toast where applicable. The addSubmitButton call is left unchanged. The excerpt does not explain why the loader package is being removed or what the re-enabled components do.