test(datepicker): Some cleaning

Well, the biggest change here is changing `$rootScope` to just `scope`.

Apart from the fact that all the others tests use `scope` and not `$rootScope`, someone who reads the tests could be confused seeing `$rootScope` (is `$rootScope` needed for this directive? it is just an extra dep?... That kind of questions :P)

On the other hand, in inject `$compile` and assign it to a global variable which is wrong. After that there is a `beforeEach` that injects `$rootScope` and `$compile` again without need.

I removed two expectations because they were already tested and a couple of typos in some strings.