Merge pull request #15930 from ryantxu/remove-kbn-test

Remove deprecated kbn test

public/app/core/specs/kbn.test.ts

-import kbn from '../utils/kbn';
-
-describe('stringToJsRegex', () => {
-  it('should parse the valid regex value', () => {
-    const output = kbn.stringToJsRegex('/validRegexp/');
-    expect(output).toBeInstanceOf(RegExp);
-  });
-
-  it('should throw error on invalid regex value', () => {
-    const input = '/etc/hostname';
-    expect(() => {
-      kbn.stringToJsRegex(input);
-    }).toThrow();
-  });
-});