Remove deprecated spectral indices

[remi-braun]

Remove the following deprecated spectral indices:

# Deprecated spectral indices: corresponding Awesome Spectral Indices 
DEPRECATED_SPECTRAL_INDICES = {
    "AFRI_1_6": "AFRI1600",
    "AFRI_2_1": "AFRI2100",
    "BSI": "BI",
    "NDGRI": "NGRDI",
    "NDRE1": "NDREI",
    "RGI": "RGRI",
    "WV_BI": "NHFD",
    "WI": "WI2015",
    "RDI": "DSI",
    "DSWI": "DSWI5",
    "GRI": "DSWI4",
    "WV_SI": "NDSIWV",
    "PANI": "BITM",
}

They have been replaced by their equivalent in Awesome Spectral Indices.