internal/frontend: remove leading slash returned by Pacakge
internal/frontend: remove leading slash returned by Pacakge

Change-Id: Ie85f1bf84f474cb8c83cf2770c8525b99bc7b4df
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/492159
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite