test: use common.expectsError()

Use common.expectsError() instead of rolling own validation function in
test-http-request-invalid-method-error.js. common.expectsError() didn't
exist when the test was written, but now it does.

PR-URL: nodejs#11408
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-http-request-invalid-method-error.js

@@ -1,12 +1,9 @@
 'use strict';
-require('../common');
+const common = require('../common');
 const assert = require('assert');
 const http = require('http');
 
 assert.throws(
   () => { http.request({method: '\0'}); },
-  (error) => {
-    return (error instanceof TypeError) &&
-      /Method must be a valid HTTP token/.test(error);
-  }
+  common.expectsError(undefined, TypeError, 'Method must be a valid HTTP token')
 );