path/filepath: do not call GetFinalPathNameByHandle from EvalSymlinks

EvalSymlinks is using GetFinalPathNameByHandle to handle symlinks with
unusual targets like \??\Volume{ABCD}\. But since CL 164201, os.Readlink
handles path like that too.

So remove all that extra code that EvalSymlinks calls when os.Readlink
fails - it is not needed any more.

Now that windows EvalSymlinks implementation is similar to unix
implementation, we can remove all slashAfterFilePathError related code
too. So do that.

This also makes TestIssue29372 pass even when TMP directory refers to
symlinks with target like \??\Volume{ABCD}\. So remove TestIssue29372
code that helped it pass on windows-arm. TestIssue29372 should pass as
is now.

Fixes #29746

Change-Id: I568d142c89d3297bff8513069bceaa6be51fe7e4
Reviewed-on: https://go-review.googlesource.com/c/164202


Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>