cmd/dist: drop testcarchive on ppc64le

It is timing out on the dashboard.
(We enabled it as an experiment to see if it was still broken. Looks that way.)

Change-Id: I425b7e54a2ab95b623ab7a15554b4173078f75e2
Reviewed-on: https://go-review.googlesource.com/23480Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/dist/test.go

@@ -680,8 +680,7 @@ func (t *tester) supportedBuildmode(mode string) bool {
 		}
 		switch pair {
 		case "darwin-386", "darwin-amd64", "darwin-arm", "darwin-arm64",
-			"linux-amd64", "linux-386", "windows-amd64", "windows-386",
-			"linux-ppc64le":
+			"linux-amd64", "linux-386", "windows-amd64", "windows-386":
 			return true
 		}
 		return false