The safefilepath package was originally added to contain
the FromFS function. We subsequently added FromFS to path/filepath
as Localize. The safefilepath package now exists only to permit
the os package to import Localize.

Rename safefilepath to filepathlite to better indicate that it's
a low-dependency version of filepath.

Change-Id: I4c5f9b28e8581f841947b48c5cac9954cd0c9535
Reviewed-on: https://go-review.googlesource.com/c/go/+/581517


LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>