remove `map_security_sectors()` once its purpose is shifted to 2DegreesInvesting/data_preparation

[cjyetman]

Once 2DegreesInvesting/data_preparation/issues/14 has been resolved, we should remove map_security_sectors(), whose purpose should be fully superseded by whatever is implemented over there.

[cjyetman]

This is also relevant to the refactoring happening in #247

[cjyetman]

also development in https://github.com/cjyetman/data_preparation/tree/input-data-validation to add validation functions and make the data_preparation code more robust is relevant