[dev.typeparams] cmd/compile: simplify walkGoDefer

[dev.typeparams] cmd/compile: simplify walkGoDefer

order already takes care of wrapping all go/defer function calls, so
there's no need for walk to duplicate that logic: it's never going to
be used.

Change-Id: I54e545404e52ab8f9d60151d1bd2aff4b9bd8b72
Reviewed-on: https://go-review.googlesource.com/c/go/+/330270
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>