Remove DOID mappings where primary mappings exist

[bgyori]

This PR removes DOID mapping predictions where DO (as a primary provider) already provides mappings to MeSH, UMLS or EFO for a given DOID. For instance, if for a given DOID, there already exists a mapping to UMLS and EFO but not the MeSH, any UMLS and EFO predictions are removed from here and any MeSH predictions here are retained.

[bgyori]

The before/after mappings counts are as follows:

DOID-MESH: 2924->451
DOID-UMLS: 8805->2467
DOID-EFO: 2267->2142

In other words, the majority of mappings to MESH and UMLS were redundant since they were already available from DO, but most of the EFO mappings are potentially non-redundant and useful.