replace or remove usages of UBERON's 'life-death temporal boundary'

[hoganwr]

UBERON intends to obsolete 'life-death temporal boundary'. See obophenotype/uberon#3488

Two options, for all the usages in symbiosis classes:

1. Replace it with 'death stage' (http://purl.obolibrary.org/obo/UBERON_0000071)
2. Remove the part of the axiom that uses it

The first option better preserves the status quo. The second option removes what some might criticize as needless complexity in the axioms.