go/internal/gcimporter: drop indexed import
The compiler hasn't emitted indexed export data files since go1.19,
so this code, which is only statically reachable from
go/importer.For("gc") aka importer.Default(), is not dynamically
reachable since those files will not be in indexed format.
Updates #68898
Change-Id: I12ea4e1b88da4fffdc9a07f318b9445a61e0d02b
Reviewed-on: https://go-review.googlesource.com/c/go/+/620135
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>