cmd/compile: remove now-irrelevant test

This test measures "line churn" which was minimized to help
improve the debugger experience.  With proper is_stmt markers,
this is no longer necessary, and it is more accurate (for
profiling) to allow line numbers to vary willy-nilly.

"Debugger experience" is now better measured by
cmd/compile/internal/ssa/debug_test.go

This CL made the obsoleting change:
https://go-review.googlesource.com/c/go/+/102435

Change-Id: I874ab89f3b243b905aaeba7836118f632225a667
Reviewed-on: https://go-review.googlesource.com/113155


Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>