go/packages: drop imports of reflect in tests of import graph
go/packages: drop imports of reflect in tests of import graph

In CL 219639 the generated testing package gets a dependency on reflect.
Trim that dependency in the go/packages tests, just as we trim
other dependencies of the generated testing package.

Updates golang/go#34129

Change-Id: I5e2578fc61cafb4d524d0a58525cf78a402c1143
Reviewed-on: https://go-review.googlesource.com/c/tools/+/221477
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Michael Matloob <4562438b12c14e81a47550acde616ff328a909f8@golang.org>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools