Remove deprecated template_file call

[labrown]

The template provider is deprecated by Hashicorp. Remove the data resource calling the template function and use calls to the builtin file function in the lambda_zip resource.

Issue #56:

Remove the template_file t_file data resource which uses the template function and update the lambda_zip resource to call the file function to get the lambda script contents directly.

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[elementalvoid]

I added the following comment to issue #64 but am copying it here for more visibility...

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#40, #57, and #65 have all been created to fix this. All three have slightly different solutions.

At a glance, #57 fixes it the cleanest way.

The source_files are not templates and do not need to be rendered in any way. I don't know why it was done that way in the beginning, but #40 continues to treat them as templates though it does switch to the built-in function. #65 removes the templating but is more complex using the local_file data source.