Remove dep_selector/Gecode

[danielsdeleo]

Description

Policyfiles no longer use the gecode solver, and Berks can optionally use molinillo. The reason we still have the gecode solver is because it's used in the Chef Server and in some cases gecode picks weird dependency solutions, so we want Berks to pick those same solutions as well. The result of this is that we eat a huge amount of pain compiling gecode everywhere just to support a workflow that's pretty broken. We should instead encourage users to find a cookbook locking mechanism that works for them (policyfiles, environments). Another way to go would be to switch Chef Server to molinillo and have a major release.

[tyler-ball]

Moving this issue to Chef Workstation. As of 0.15.18 we still pull in gecode so this is still applicable.