Cognito unused variables

[jarajapu]

To do -

• see if it makes sense to remove the following vars from variables
• remove them from README
• remove them from module instances in both US and NLD apps
• test both US and NLD contexts to make sure nothing breaks

ecr_name_suffix: (string) Default is "app". Suffix for the ECR name.
ssm_name_prefix: (string) Should be '/{project}/{environment}'.
cognito_region: (string) The region where the user pool is created.
cognito_email_verification_message: (string) Email verification message.
cognito_email_verification_subject: (string) Email verification subject.
cognito_admin_create_user_message: (string) Admin create user message.
cognito_allow_email_address: (string) Allow email address for Cognito.