Since CL 194600, search.CleanPaths preserves characters after '@' in
each argument. This was done so that paths could be cleaned while
version queries were preserved. However, local and absolute file paths
may contain '@' characters.

With this change, '@' is treated as a normal character by
search.CleanPaths in local and absolute paths.

Fixes #35115

Change-Id: Ia7d37e0a2737442d4f1796cc2fc3a59237a8ddfe
Reviewed-on: https://go-review.googlesource.com/c/go/+/202761
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>