scripts: remove dependency on AWS_ environment variables

## Problem

some scripts will fail if `AWS_ACCESS_KEY_ID` or `AWS_SECRET_ACCESS_KEY` are not set.

for example

https://github.com/algorand/go-algorand/blob/d3c10f41f2ac3e2bf84d8ddfd134c1cfba3d0908/scripts/create_and_deploy_private_version.sh#L24-L27

https://github.com/algorand/go-algorand/blob/d3c10f41f2ac3e2bf84d8ddfd134c1cfba3d0908/scripts/create_and_deploy_recipe.sh#L25-L28

https://github.com/algorand/go-algorand/blob/d3c10f41f2ac3e2bf84d8ddfd134c1cfba3d0908/scripts/deploy_linux_version.sh#L43-L46

this limits one's ability to use more secure means of authenticating with AWS, e.g. EC2 metadata or IRSA.

## Solution

remove these checks. if it's still desired to have an AWS check, use `aws sts get-caller-identity` to determine if the shell is configured properly for AWS communication. this is appropriate because utlimtaely the scrips use the aws cli to communicate with S3.