Unwind-to-frame-and-call-VOP doesn't need static symbols.
* The UNWIND procedure takes as parameters a target block and an
unknown-values start/count pair. The old implementation was passing
the block, a zero count, and a garbage start. Pass the function to
call as the start, instead of storing it as a static symbol value as
is done now or reserving an extra stack slot somewhere relative to
the unwind block.
* Delete the static symbol formerly used for this.