Ports Mind Procs from NT

ports some mind procs I made ages ago for NT

remove_antag() is primarily to reduce the clutter in the Topic() but can be used on any mind and antag.
remove_all_antag() is for lazy people, might have like, 1 genuine use.
wipe_memory() is just a shortcut to memory = null.

Testing: Been live on Artyom and NT for about 1 1/2 months with no issues.


Use constants, not magic strings.