internal/bytealg: remove aix and linux build tags from ppc64 index code

This code is generic to ppc64/ppc64le - there is no need to limit it to
aix or linux.

Updates #56001

Change-Id: I613964a90f9c5ca637720219a0260d65427f4be0
Reviewed-on: https://go-review.googlesource.com/c/go/+/473697


TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Joel Sing <joel@sing.id.au>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>

src/internal/bytealg/index_ppc64x.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build (aix || linux) && (ppc64 || ppc64le)
+//go:build ppc64 || ppc64le
 
 package bytealg