cmd/compile/internal/reflectdata: remove special case for init

cmd/compile/internal/reflectdata: remove special case for init

Now that package initialization ordering is handled by types2 instead
of pkginit, we can get rid of this special case.

Change-Id: I4b94df02813b662498ae7d2e829119e3bb932d6e
Reviewed-on: https://go-review.googlesource.com/c/go/+/520604
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>