Remove the 99999 macro arg limit

[Rangi42]

This limit was never documented, and was basically a convenience in C because allocating memory for all those args was handled manually. Now they're just in a std::vector, and this check feels more like cruft than an actual safety mechanism.

(It's possible for a vector to OOM, of course, but we have plenty of other places that risk that. The parser has many values which unboundedly build up a vector, like charmap multi-values, purged symbols, or ds N, ... expressions. Nobody is actually ever going to get near the machine limits.)