This change deletes several internal packages, replaces imports to
them with the equivalent golang.org/x/mod packages, updates x/mod, and
re-runs 'go mod vendor'.

Packages are replaced as follows:

cmd/go/internal/modfile → golang.org/x/mod/modfile
cmd/go/internal/module → golang.org/x/mod/module
cmd/go/internal/semver → golang.org/x/mod/semver
cmd/go/internal/sumdb → golang.org/x/mod/sumdb
cmd/go/internal/dirhash → golang.org/x/mod/sumdb/dirhash
cmd/go/internal/note → golang.org/x/mod/sumdb/note
cmd/go/internal/tlog → golang.org/x/mod/sumdb/tlog

Updates #31761
Fixes #34924

Change-Id: Ie3bf677bb0be49af969f654a0214243a6547eb57
Reviewed-on: https://go-review.googlesource.com/c/go/+/202698
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>