Use aws_s3_get for s3cache instead of aws transfer library

[jpswinski]

The s3cache I/O driver currently uses the aws transfer library, but it should probably be replaced by a version of the much simpler aws_s3_get function used by Lua.

Performance tests will need to be run using both versions of the code. The advantage of not using the transfer library is that it will simplify the dependencies when building SlideRule. The aws_s3_get code is also a lot easier to understand.

[jpswinski]

The S3CurlIODriver implements a aws-sdk-less get for S3 data and is now being used for the cache driver.