Simplify DSLX proc syntax

Example of curent syntax

```
pub proc foo {
in_ch: chan in;
out_ch: chan out;

init { () }

config (i: chan in, o: chan out) {
let (a_in, a_out) = chan;
spawn bar(a_in);
spawn qux(a_out);
(i, o)
}

next(tok: token, state: ()) {
// use in_ch and out_ch
}
}
```

There is a fair amount of replication and boiler plate in the config. One alternative might be to have the proc config arguments defined by the proc name kind of like a function. The config could even be folded up into the proc body. Maybe something like:

```
pub proc foo(in_ch: chan in, out_ch: chan out) {
let a = chan;
spawn bar(a.in);
spawn qux(a.out);

init { () }

next(tok: token, state: ()) {
// use in_ch and out_ch
}
}
```

This example uses #830 in which channels declarations produce structs with in and out members,