Remove Podfile.lock

I don't think its necessary to lock the dependencies in this project, it doesn't matter what versions of the dependencies are used in testing since this isn't production app.

It's a little cumbersome to ensure the lockfile is in-sync than the benefits it's worth.

Otherwise when you change the pod spec, such as in https://github.com/orta/ORStackView/commit/601d52432c112960aa1c4edf7db4ced44f2d7515#diff-7a23f687cbd9f0cee14ce063780aee69 the hash will change. So you will need to run `pod update` from the Project else the hash in the lock file will differ and `pod install` will not work.

Related to https://github.com/AFNetworking/AFNetworking/pull/1445