Revert "go/types, types2: only use fileVersion if 1.21 or greater"
This reverts CL 603895
Reason for revert: We've decided to change the logic for how upgrades are done and want to submit the new logic in a self contained CL that can be cherry-picked onto release-branch.go1.23
Change-Id: I366af8e95ce1de7311b0385a23f9dd3df175745a
Reviewed-on: https://go-review.googlesource.com/c/go/+/605675 Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>