Remove getAjaxVersion().

It was very specific to prototype, which has a very low adoption rate
these days.

/**
 * testRequestClientTypes method
 *
 * @return void
 */
	public function testRequestClientTypes() {
		$this->RequestHandler->request->env('HTTP_X_PROTOTYPE_VERSION', '1.5');
		$this->assertEquals('1.5', $this->RequestHandler->getAjaxVersion());

		$this->RequestHandler->request->env('HTTP_X_REQUESTED_WITH', false);
		$this->RequestHandler->request->env('HTTP_X_PROTOTYPE_VERSION', false);
		$this->assertFalse($this->RequestHandler->getAjaxVersion());
	}
Merge pull request #4094 from cakephp/remove-getajax-version

Remove getAjaxVersion().