eliminate LEAVESUB() macro

eliminate LEAVESUB() macro

Many years ago, POPSUB was split into two parts, with a final cleanup
being done by the LEAVESUB() macro. After the previous commit, LEAVESUB
now always immediately follows POPSUB, so roll its action into the
last line of POPSUB and eliminate it.

This also allows us to remove the 'sv' parameter from POPSUB(), which
was needed purely to communicate to LEAVESUB() which var to process