[dev.link] cmd/internal/objfile: read Go object file using goobj2 package

[dev.link] cmd/internal/objfile: read Go object file using goobj2 package

Read Go object files using cmd/internal/goobj2 package directly,
instead of using cmd/internal/goobj as an intermediate layer.

Now cmd/internal/archive is only about reading archives.

Change-Id: Ifecb217fb26c16c26fc1bbc3fba0ed44710020ed
Reviewed-on: https://go-review.googlesource.com/c/go/+/246443
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>