misc/cgo/testcarchive: remove special flags for Darwin/ARM

misc/cgo/testcarchive: remove special flags for Darwin/ARM

The original Darwin/ARM port is gone. For ARM64, it works fine
without the flags on macOS/ARM64. Remove the flags.

Change-Id: I9cc00c49dd71376dd9c52abb78c2d8cec656b3db
Reviewed-on: https://go-review.googlesource.com/c/go/+/280157
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>