[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


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