Remove obsolete :mock and :meck dependencies

[kmakiela]

This PR removes :meck and :mock from the dependency list.
Both :meck and :mock are not needed anymore. All the tests that used these libraries were already rewritten (most of them use :mox now).

[NelsonVides]

So cool it would be so simple to get rid of Mock 😄
But what about the mix.lock file, doesn't that one need to be cleaned out as well?

[michalwski]

@kmakiela I second @NelsonVides questions. Looks like mix.lock needs an update.

[kmakiela]

Further investigation shows that :meck is still loaded as a Sparrow dependency (and Sparrow only) so this PR is temporarily blocked by:
esl/sparrow#47

[NelsonVides]

@kmakiela esl/sparrow#47 was merged, we can move forward with this one 🙂

[NelsonVides]

Neat 🎉