refactor: delete containsRegexp() (there is escapeRegExp() in the lang facade)

BREAKING CHANGES:

`containsRegexp` is no more exported from `@angular/core/testing`. It should not have been part of the public API in the first place.

modules/@angular/core/testing/regexp.ts

@@ -1,9 +0,0 @@
-import {RegExpWrapper, StringWrapper} from '../src/facade/lang';
-
-var _RE_SPECIAL_CHARS =
-    ['-', '[', ']', '/', '{', '}', '\\', '(', ')', '*', '+', '?', '.', '^', '$', '|'];
-var _ESCAPE_RE = RegExpWrapper.create(`[\\${_RE_SPECIAL_CHARS.join('\\')}]`);
-export function containsRegexp(input: string): RegExp {
-  return RegExpWrapper.create(StringWrapper.replaceAllMapped(
-      input, _ESCAPE_RE, (match: any /** TODO #9100 */) => `\\${match[0]}`));
-}