Decide to drop MS:'electrospray ionization' in favor of the already existing CHMO:'electrospray ionisation'

As noted in 411649c it seems that the MS class is not needed anymore and the native CHMO one should be used instead. Although MS is part of OBO, I'd argue against reusing it in CHMO, as the hierarchy and axiomatization of MS is not done according to best practices used in other OBO ontologies. I would rather only link to it using annotations on the CHMO equivalent.