chore: remove redundant six usage

[mndeveci]

Address issues from earlier PR: #248 (review)

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[jfuss]

Can we remove six all together?

Would require removing the dep: https://github.com/aws/aws-lambda-builders/blob/develop/requirements/base.txt and from these spots as well: https://github.com/aws/aws-lambda-builders/search?q=six. Looks like the only usage is six.string_types which can be replaced by str.

[mndeveci]

Can we remove six all together?

Would require removing the dep: https://github.com/aws/aws-lambda-builders/blob/develop/requirements/base.txt and from these spots as well: https://github.com/aws/aws-lambda-builders/search?q=six. Looks like the only usage is six.string_types which can be replaced by str.

I followed this website to remove all six usage: https://python-future.org/compatible_idioms.html#metaclasses

I am not sure if we need to keep object as base class here;
class BaseAction(object, metaclass=_ActionMetaClass)

Let me know if that is redundant.

[jfuss]

I am not sure if we need to keep object as base class here;
class BaseAction(object, metaclass=_ActionMetaClass)

I am not sure either and would rely on our tests for validation here. Without reading more deeply, this seems fine.