Revert part of r193291, restoring the deletion of loaded objects.

Revert part of r193291, restoring the deletion of loaded objects.
Without this, customers of the MCJIT were leaking memory like crazy.

It's not really clear what the *right* memory management is here, so I'm
not trying to add lots of tests or other logic, just trying to get us
back to a better baseline. I'll follow up on the original commit to
figure out the right path forward.

llvm-svn: 193323