Remove GPy

**Describe the bug**
The GPy dependency does not work anymore for python>=3.8

**To Reproduce**
Run LocalAS 

**Output**
`AttributeError: module 'numpy' has no attribute 'bool'`

**Proposed solution**
Use scikit implementation instead: [GaussianProcessRegressor](https://scikit-learn.org/stable/modules/generated/sklearn.gaussian_process.GaussianProcessRegressor.html)
