fix(editcheck): the revived Ruby branch is inert, and the comment now says which one

PR #47 listed editcheck.h's implicit-receiver exemption as a dead branch its scope arm
revives. It does revive it — and the branch is still unreachable, for a second and
independent reason the note did not mention: Ruby's `def m(a)` has no implicit receiver
parameter to exempt, and the caller test short-circuits on `arityExact == 0`, which
cc_paramArityExact hands every Ruby definition because its language gate does not list
Ruby. Measured on a two-file Ruby repo whose method gained a parameter: incompatible="0"
for a scoped method and a top-level one alike, before and after the scope arm.

What the scope arm actually bought --edit-check is the SELECTOR, which is worth having:
`--edit-check=Widget::resize` answered "symbol not found" before it and returns a full
contract verdict (params_was=1 params_now=2, callers=1) after. Both facts recorded where
the predicate lives, so the next reader is not told a signal was recovered when none was.