remove duplicated length check
remove duplicated length check

not only it was duplicated, it also could be considered harmful
for cases when an optional named argument was omitted

the correct places for that check are getTypeArg and getTypeArgDefault where we
know we're working with positional arguments that cannot be omitted

refers #117

errx/carbonapi,arodland/carbonapi,errx/carbonapi,dgryski/carbonapi,nnuss/carbonapi