cmd/compile/internal/inline: remove useless code

cmd/compile/internal/inline: remove useless code

There doesn't appear to be any need for this code. EditChildren won't
recurse into the closure body anyway.

Split out into a separate commit in case I'm overlooking something.

Change-Id: I004d1aa04865896de972bf3323b1622cc08a0d18
Reviewed-on: https://go-review.googlesource.com/c/go/+/543659
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>