FIX: Dataset exclusion query for duplicated excluded model contributions

[bocklund]

If a fixed site fraction dataset has duplicated excluded model contributions, (which can happen if applying the same contribution in two different tags, for example), e.g.

{
    "components": ["CU","MG"],
    "phases": ["CUMG2"],
    "solver": {
        "mode": "manual",
        "sublattice_site_ratios": [1,2],
        "sublattice_configurations": [["CU","MG"]]
    },
    "conditions": { "P": 101325, "T": 298.15},
    "output": "SM_FORM",
    "values": [[[-4.4]]],
    "reference": "Estimated from Zhou (2007)",
    "bibtex": "zhou2007",
    "comment": "Estimated from enthalpy by s=h/3000",
    "excluded_model_contributions": ["idmix", "mag", "idmix", "mag"]
}

the current behavior of the code will result in the excluded model contribution query failing and the dataset gets filtered out.

This change resolves that behavior.

• Needs a test to be merged