Revert "[WebDriver] throw exception if XPath is malformed"

This reverts commit 856988545d1c34429df135f743fdd14ffd5addfa.
Revert "Risky tests are supposed to be errors. Fix #1373"

This reverts commit c64e59ae1ff0bb7804e503a3332b41f636f20d50.
inner browser returns empty array on malformed xpath