go/internal/gcimporter: enable importing typeparam/issue48424.go

This is a partial revert of CL 353389, now that go/types supports
eliding interface in constraints.

For #48424

Change-Id: Ibde26fb66bf6bd5a4c919acffd045a57783d1b47
Reviewed-on: https://go-review.googlesource.com/c/go/+/354990


Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>