[release-branch.go1.22] crypto/x509: remove TestPlatformVerifierLegacy tests

They are no longer necessary, woohoo!

Updates golang#52108
Fixes golang#56791
Fixes golang#67352

Change-Id: I11a4c17162da4295309f74f2f8362bab0f506f78
Reviewed-on: https://go-review.googlesource.com/c/go/+/548976
Run-TryBot: Roland Shoemaker <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Roland Shoemaker <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
(cherry picked from commit c1828fb)
Reviewed-on: https://go-review.googlesource.com/c/go/+/586235
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: rolandshoemaker