internal/syscall/unix: remove superfluous var declarations in {Unlink,Open}at
internal/syscall/unix: remove superfluous var declarations in {Unlink,Open}at

Change-Id: Id58e3aebf325433768675523bf34c0b7e0e34aea
Reviewed-on: https://go-review.googlesource.com/c/go/+/431235
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Reviewed-by: Jenny Rakoczy <6a3f4389a53c889b623e67f385f28ab8e84e5029@golang.org>
Auto-Submit: Jenny Rakoczy <6a3f4389a53c889b623e67f385f28ab8e84e5029@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go