Changes "was loaded as" to "was required as". This is slightly more
precise, since it hints at a requirement edge in the module version
graph.

Updates #28489

Change-Id: I636268c33f1ea9858c214fe275f271538186ed6d
Reviewed-on: https://go-review.googlesource.com/c/go/+/186377
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>