Fix deadline inference, test GEDF, and remove chain ID

[edwardalee]

This PR fixes deadline propagation. Previously, a reaction would inherit the deadline of a downstream reaction only if there was a data path through ports to the downstream reaction. This corrects this so that a reaction that is lexically earlier than another reaction in a reactor inherits the deadline of that later reactor.

This PR also adds the test PR 426 of reactor-c that checks for correct behavior of the GEDF scheduler. It also updates reactor-c to include the corrected GEDF scheduler.

This PR also gets rid of the chain_id, which never worked.

[petervdonovan]

I think this PR is good to merge. The inferred deadline algorithm looks right to me, and I am happy that PeriodicTask checks execution order using physical time instead of using a global variable.

[lhstrh]

@edwardalee: After lf-lang/reactor-c#426 has been merged, I'll update reactor-c with an interactive rebase and clean up the history.

[lhstrh]

I wasn't able to do a full rebase without going through too much trouble because merges with master had already happened along the way, so I just did a small few fixups... But reactor-c points to main now.