cmd/link: remove support for darwin/386 relocations
The darwin/386 port has been unsupported for years, but some
relocation handling specific to it has managed to survive till now.
Updates #37610
Change-Id: I27ae2ac5462c5f3ec219e9cb5dce6f83b037b816
Reviewed-on: https://go-review.googlesource.com/c/go/+/703777 Reviewed-by: Michael Knyszek <mknyszek@google.com> Reviewed-by: Than McIntosh <thanm@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>