Revert "start experimental implementation of revised new_specification"

This reverts commits 7f58ad8, eae01bc, and c07a105.
Add gen_new_specification and remove prim_constant_definition

Implement new_definition in terms of gen_prim_specification.
Leave the existing new_specification in place.
This plan of attack suggested by RDA.

Have only touched the standard kernel, and none of the theories.
Next steps would include updating the other kernels, implementing
new_specification in terms of gen_new_specification (at some point after
pairTheory), and removing uses of new_specification before pairTheory
one by one if possible/desired...