Remove without-interrupts from runtime/global.scm.

Remove without-interrupts from runtime/global.scm.

Clean-obarray runs as a secondary-gc-deamon and thus, in SMPing
worlds, it may run in parallel with other threads on other processors.

A number of primitives and compiler utilities modify the obarray so an
SMPing microcode will use a pthread mutex to serialize access to it.
Clean-obarray now uses a new procedure, with-system-obarray-lock, that
uses new primitives to participate in the serialization.

Remove limit-interrupts!.  Like without-interrupts, it will not work
as expected in SMPing worlds.