[bugfix] Exise speed attribute from monster.

Fixes being unable to hit monsters due to superspeed as reported at http://smf.cataclysmdda.com/index.php?topic=7771
Fixes #8991 
Fixes #9006 
The fix is super long, because there was actually a huge latent bug in that the transition from using monster::speed to creature::get_speed() and friends was stopped part way through, so roughly half the code was using one, and half was using the other.
This was triggered by BevapDin's save/load streamlining, because the old code was actually saving/loading more than it should have and hiding this bug.
The extra good news is that it didn't mutate any values, so it's a rare save/load bug that will go back to normal after applying the fix.