cmd/compile: remove reportTypeLoop

cmd/compile: remove reportTypeLoop

reportTypeLoop used to be used to report invalid recursive types in old
typechecker.

However, types2 now reports this error, so this can be removed.

Updates #51691

Change-Id: I5e73369dadafb0cc56e682668b32cbd1e1210f2f
Reviewed-on: https://go-review.googlesource.com/c/go/+/394554
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>