Record calls to vararg functions.

This loop is now roughly 1000x faster than the Lua interpreter:
  local function f(a,b,...) end; for i=1,2e8 do f(1,2,i) end
Yet another silly microbenchmark -- I know.

src/lj_traceerr.h

@@ -23,7 +23,6 @@ TREDEF(BADTYPE,	"bad argument type")
 TREDEF(CJITOFF,	"call to JIT-disabled function")
 TREDEF(CUNROLL,	"call unroll limit reached")
 TREDEF(DOWNREC,	"down-recursion, restarting")
-TREDEF(NYIVF,	"NYI: vararg function")
 TREDEF(NYICF,	"NYI: C function %p")
 TREDEF(NYIFF,	"NYI: FastFunc %s")
 TREDEF(NYIFFU,	"NYI: unsupported variant of FastFunc %s")