JIT: Clean up float loads and stores.

Less code is good, and this should make future changes to memory handling
easier.
JIT: Remove dead code.
JITIL: fix some unsafe loads.

I'm planning on making changes to the memory code, so I don't want this
stuff to get in the way.  The slight performance hit to JITIL isn't really
important at the moment.
JIT: Make lmw/stmw use safe load/stores.