sagemathgh-37115: Remove check for deprecated attribute _no_generic_b…

…asering_coercion

    
In `sage.categories.unital_algebras.UnitalAlgebras`, remove the check
for the attribute `_no_generic_basering_coercion`, which was deprecated
in sagemath#19225. This means that this attribute is now completely ignored by
the coercion framework.
    
URL: sagemath#37115
Reported by: Peter Bruin
Reviewer(s): Marc Mezzarobba