[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.
This should probably set the base speed. The speed bonus is reset and lost at the end of the turn, so every blob ends up with the default speed again. The above should also test the local variable speed, not z->get_speed, because the local variable has been reduces by a random amount and the previous code used the local variable.