Remove deprecated `boost` parameter from the mapping

[Chunlei Wu]

boost settings in the mapping (index time boosting) is deprecated, are removed in ES8. Field-level boosting should be specified at the query time.

https://www.elastic.co/guide/en/elasticsearch/reference/7.17/mapping-boost.html

An example from MyGene.info (there are other places too):

mygene.info/src/hub/dataload/sources/ensembl/gene_upload.py

Lines 34 to 36 in e94ea45

 "name":   {"type": "text", 
            "boost": 0.8,    # downgrade name field a little bit 
            'copy_to': ['all'],}, 

We should remove these boost settings from the mapping in all MyGene.info data sources.