[PAM] Remove unnecessary reqwest error checks

It seems all 4xx errors are pushed into ServerResponse

src/pam.rs

@@ -85,13 +85,8 @@ fn do_legacy_auth(username: String, password: String, config: Config) -> Result<
             Err(e) => match e {
                 RequestTokenError::Request(re) => match re {
                     reqwest::Error::Reqwest(ree) => {
-                        if ree.is_status() {
-                            error!("Authentication failed for invalid grant: {}", ree);
-                            return Err(PamError::AUTH_ERR);
-                        } else {
-                            error!("Request error requesting token: {}", ree);
-                            return Err(PamError::AUTHINFO_UNAVAIL);
-                        }
+                        error!("Request error requesting token: {}", ree);
+                        return Err(PamError::AUTHINFO_UNAVAIL);
                     },
                     reqwest::Error::Http(he) => {
                         error!("HTTP error requesting token: {}", he);