Drop use of maap-py for obtaining S3 credentials

[chuckwondo]

S3 credentials are now obtained via a role using EC2 instance metadata. In addition, removed HTTP retry logic since all granules are now obtained via S3 only.

Fixes #14

[wildintellect]

I'm generally in favor of this for actual MAAP usage, but have concerns about removing the functionality to operate in a different way given the possibility of wanting to us this outside of MAAP, e.g. VEDA.
That would favor dropping maap-py but I wonder if we can more generically make AWS credentials modular to allow several options for obtaining (e.g. EarthAccess)

[chuckwondo]

I'm generally in favor of this for actual MAAP usage, but have concerns about removing the functionality to operate in a different way given the possibility of wanting to us this outside of MAAP, e.g. VEDA. That would favor dropping maap-py but I wonder if we can more generically make AWS credentials modular to allow several options for obtaining (e.g. EarthAccess)

Yes, there is a separate issue for refactoring for use outside of MAAP. When I work on that issue, I'll sort out how to make this modular. At the moment, I feel this simplification will better enable introducing modularization later. There will be less cruft to deal with.

[chuckwondo]

@wildintellect and @jjfrench, I've taken this PR out of Draft. It is now ready for review. I registered gedi-subset:issue14-auto-refresh-s3-creds and confirmed that it works.

[jjfrench]

Lookin good, thanks!