Remove test assertion of the TimeoutException message wording

The message itself comes from the php-websocket library, and
the wording depends on the installed version (it has changed
in phrity/websocket:1.7.0).

In the past, chrome-mink-driver had runtime code which depended
on the exact wording of this exception but that was removed in
4365fc4 - the message text is no longer relevant to this
package so there is no need to couple the tests to the internals
of php-websocket.

tests/ChromeDriverConnectionTest.php

@@ -39,7 +39,6 @@ public function testTimeoutExceptionIfResponseBlocked()
         ];
         $this->driver = new ChromeDriver('http://localhost:9222', null, 'about:blank', $options);
         $this->expectException(TimeoutException::class);
-        $this->expectExceptionMessage('Client read timeout');
         $script = "confirm('Is the browser blocked? (yes, it is)');";
         $this->driver->visit('about:blank');
         $this->driver->evaluateScript($script);