remove as_str() legacy wrappers, callers use .into() directly

swarm-secret-client/src/policy.rs

@@ -54,7 +54,7 @@ pub fn hive_object_name(hive: &str) -> Result<String, Error> {
 pub fn render() -> String {
     format!(
         "path \"{MOUNT}/data/{ROOT}/{}/*\" {{\n  capabilities = [\"read\"]\n}}\n",
-        Kind::Agent.as_str()
+        <&str>::from(Kind::Agent)
     )
 }