Prune ALLOW_ADD_IN_MSG and ALLOW_DEL_IN_MSG options

Summary:
Options ALLOW_ADD_IN_MSG and ALLOW_DEL_IN_MSG have been commented out
in the code in the @onefang rewrite, but artefacts were left int the
source code.

Test Plan: Recompile, assert the symbols aren't used

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D876