cmd/go: re-enable go/types requirement during vet during go test

[rsc]

@griesemer has some reports that go/types fails on some code during automatic vet-during-test. We should make a type-checking failure during vet-during-go-test a silent vet success instead (we know the code compiles, so we know vet is at fault), but vet-during-go-vet should still fail.

[griesemer]

For the reference: The offending go/types issue is #18395 (plus a few duplicates).

[mvdan]

Should a warning of some sort be printed? Otherwise, the user might get the wrong idea that there are no vet warnings at all.

[gopherbot]

Change https://golang.org/cl/81500 mentions this issue: cmd/go: ignore vet typecheck failure during go test

[rsc]

The CL is in, so vet no longer dies. Repurposing this issue for removing the check once we believe go/types is safe to require (hopefully for Go 1.11).

[mvdan]

This is marked as early-in-cicle for 1.11 - do we still want to do this in the current cycle?

[ianlancetaylor]

This was done by https://golang.org/cl/108555, so closing.