Fixed ''Unable to execute UPDATE statement [UPDATE  SET ]' exception in ...

...test suite.

On my machine (PHP 5.3.21) I get following in the unit tests:

     There was 1 failure:

     1) SortableBehaviorTest::testShiftRank
     Failed asserting that exception message 'Unable to execute UPDATE statement [UPDATE  SET ] [wrapped: Invalid argument supplied for foreach()]'
     contains 'Unable to execute UPDATE statement [UPDATE  SET ] [wrapped: Undefined index: ]'.

After fixing this invalid SQL generation, the test on a exception in `testShiftRank` is not necessary anymore. Thus, I've removed the `@expectedException*` stuff.