[dev.typeparams] runtime: undo go'd closure argument workaround

In CL 298669 we added defer/go wrapping, and, as it is not
allowed for closures to escape when compiling runtime, we worked
around it by rewriting go'd closures to argumentless
non-capturing closures, so it is not a real closure and so not
needed to escape.

Previous CL removes the restriction. Now we can undo the
workaround.

Updates #40724.

Change-Id: Ic7bf129da4aee7b7fdb7157414eca943a6a27264
Reviewed-on: https://go-review.googlesource.com/c/go/+/325110


Trust: Cherry Mui <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>