archive/zip: remove unused File.descErr field
archive/zip: remove unused File.descErr field

Found via staticcheck. Unused as of CL 357489.

Change-Id: I3aa409994ba4388912ac7e7809168529a5b6e31c
Reviewed-on: https://go-review.googlesource.com/c/go/+/403814
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Run-TryBot: Kale B <17bfab9228b6064e555c408e6372332e93a0a33a@lemnisys.com>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Auto-Submit: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Reviewed-by: David Chase <ae171625adc8645b8b79b7e405a6da5aba5341e0@google.com>

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