cmd/pprof: pprof update from upstream broke plan9 builders

[ALTree]

Possibly just a matter of skipping a test that cannot work on plan9, but not sure so I'm reporting this here. It's TestHttpsInsecure, it also caused issues on nacl.

--- FAIL: TestHttpsInsecure (11.18s)
	fetch_test.go:420: fetchProfiles(https+insecure://127.0.0.1:60968/debug/pprof/profile) got non-symbolized profile: len(p.Function)==0
	fetch_test.go:376: Serve got error accept tcp 127.0.0.1:60968: open /net/tcp/22/listen: '/net/tcp/22/listen' listen hungup, want "use of closed"

https://build.golang.org/log/c580a1b0a553f12becec023170a273efca122a08

cc @0intro

[ALTree]

Fixed by CL 75870.