Clean up droptofloor() macro hacks and clarify naming

Clean up droptofloor() macro hacks and clarify naming

It wasn't clear at call sites that this had been changed to a delayed
function (in SVQC only), and that the return value was no longer
available. We can just use different names for the QC implementation,
with different names for delayed and direct calls, and leave the
original name for calling the builtin if required. The builtin's wrapper
macro for changing the self global to a parameter is retained and it now
works the same in SVQC and CSQC.

Removes another case of cc83c39c27ea0757cf169562428e443c5ab60fdc