This matches longstanding compiler behavior.
Also, for unused packages, report:
`"pkg" imported and not used`
`"pkg" imported as X and not used`
This matches the other `X declared and not used` errors.
For #55326.
Change-Id: Ie71cf662fb5f4648449c64fc51bede298a1bdcbf
Reviewed-on: https://go-review.googlesource.com/c/go/+/432557
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>