fix: remove handler callback argument

[everett1992]

Middy does not support callback handlers since 1.x, the third argument is actually the timeout signal.

Fixes #1164

[willfarrell]

Thanks for the PR!

[phmasek]

@willfarrell this commit breaks the typing. It's not possible to seamlessly use middy with Lambda handlers as the Lambda handler is expecting the third argument to be of type Callback but it's now replaced with the incompatible type MiddyHandlerObject. Please see print screen. This is further described in issue #1176. This is the reason I added a pull request #1186.

We're currently using "@types/aws-lambda": "^8.10.136" and "aws-lambda": "^1.0.7".

The only solution I know of now is to unwrap the function and adjust the provided arguments as shown below, which might be considered a bit unrefined:

export const handler = middy<APIGatewayProxyEvent>((event, context) => {
  return lambdaHandler(event, context, () => undefined);
});