SI-7711 Do not emit extra argv in script body

Take away `argv` and make `args` the standard parameter name.

This is a quick fix to avoid "unused local" lint error.  All
the examples use `args`; in particular, "Step 4. Write some
Scala scripts" in "Programming in Scala" uses `args`.

I see the footnote there is also where Odersky concatenation is
specified, `"Hello, "+ args(0) +"!"` with no space next to the
literals.

Also removes `argv` from `StdNames`. Was torn whether just to
add `argc`. Maybe start a new project to house Names, emeritus.