chore(short-name-length-audit): remove dead code (#2517)

lighthouse-core/audits/manifest-short-name-length.js

@@ -23,19 +23,6 @@ class ManifestShortNameLength extends Audit {
     };
   }
 
-
-  static assessManifest(manifestValues, failures) {
-    if (manifestValues.isParseFailure) {
-      failures.push(manifestValues.parseFailureReason);
-      return;
-    }
-
-    const themeColorCheck = manifestValues.allChecks.find(i => i.id === 'hasThemeColor');
-    if (!themeColorCheck.passing) {
-      failures.push(themeColorCheck.failureText);
-    }
-  }
-
   /**
    * @param {!Artifacts} artifacts
    * @return {!AuditResult}