Removed an unneccessary function

Removed 'pop_keep' from 'proof_context.ml'/'proof_table.ml'

	modified:   ocaml/proof_context.ml
	modified:   ocaml/proof_context.mli
	modified:   ocaml/proof_table.ml
	modified:   ocaml/proof_table.mli
Removed commented out code

	modified:   ocaml/proof_context.ml