Drop support for "where" in HDF files

[afrubin]

Support for SQL-like operations using the where kwarg is exposed nicely by pandas but ties us to PyTables and isn't supported by dask.

In the existing code, this is only used by a few scoring methods to get information on the wild type variant. I don't know that anyone but me really used it for post-Enrich2 analysis, so it seems like a good idea to drop this support.

The main advantage of dropping this feature is that we will be more compatible with HDF5 implementations in other languages. The indexes that PyTables adds to enable the SQL-like operations make the HDF5 files look really weird when opened in R, for example.