Remove URI parameter in AWSCredentialProvider constructors

This was from comment in HADOOP-13252.
It looks like the URI parameter is not needed for our AWSCredentialProvider constructors. This was useful because we relied on URI parameter for retrieving user:pass. Now in binding URIs, we have

279 S3xLoginHelper.Login creds = getAWSAccessKeys(binding, conf);
280	      credentials.add(new BasicAWSCredentialsProvider(
281	              creds.getUser(), creds.getPassword()));

This way, we only need configuration object (if necessary) for all AWSCredentialProvider implementations. The benefit is that, if we create AWSCredentialProvider list for DynamoDB, we don't have to pass down the associated file system URI. This might be useful to S3Guard tools.