remove unused ansible vars

[melange396]

after a production release of #1926 (as part of #1935) AND a successful AWS bucket migration, we can probably take these out of the list of variables:

covidcast-indicators/ansible/vars.yaml

Lines 21 to 22 in c0fa7ef

	delphi_aws_access_key_id: "{{ vault_delphi_aws_access_key_id }}"
	delphi_aws_secret_access_key: "{{ vault_delphi_aws_secret_access_key }}"

care should be taken to ensure theyre not still being used anywhere!