cmd/compile: remove selectnbrecv2

Previous CL did remove selectnbrecv2 in runtime, the compiler now only
call selectnbrecv, so remove this. Make this as separated CL because it
adds much of noise to git stat.

Change-Id: I06e89c823c0403e9bd66f2633409c455a46d6e79
Reviewed-on: https://go-review.googlesource.com/c/go/+/292891


Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>