Test template defaults

When testing a template’s behavior, avoid overriding it with explicit parameter values. Remove parameter values from the parameters file so the template’s defaultValue(s) are used, ensuring the default-path is actually exercised.

Example (parameters file):

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentParameters.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "someParam": {
      "// omit "value" here to use template defaultValue"
    }
  }
}

Only provide value fields when intentionally testing non-default behavior; otherwise leave them out to validate defaults.