Revert "cmd/compile: restore test/nested.go test cases"

Revert "cmd/compile: restore test/nested.go test cases"

This reverts CL 424854.

Reason for revert: broke misc/cgo/stdio.TestTestRun on several builders.

Will re-land after CL 421879 is submitted.

Change-Id: I2548c70d33d7c178cc71c1d491cd81c22660348f
Reviewed-on: https://go-review.googlesource.com/c/go/+/425214
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>