Increase anubis guard Dispel Undead frequency.

Playtesting on a few devs' part suggests they weren't dispelling enough
previously, meaning they weren't consistently a threat to undead
players.

This doubles the frequency, which may be too much - but better to err on
the side of killing more players, I say.
Adjust frequencies of replacement of Tomb guardian mummies.

Each vault/subvault now picks one of three replacement sets for the
glyphs formerly corresponding to guardian mummies - one each for
ushabtiu, anubis guards, and death scarabs - and there is code in place
to ensure an even frequency distribution between the three of them on a
per-vault/subvault basis.
Redistribute random guardian mummy replacement generation weights, too.

This is a really rough reportioning, but it should work decently.