pack/ee: delete unnecessary nil checks
pack/ee: delete unnecessary nil checks

Followon to CL 1295.

Change-Id: I9da94a1ae49a436ebd461ec2fdfb5501660a6f79
Reviewed-on: https://upspin-review.git.corp.google.com/1310
Reviewed-by: Eric Grosse <f6ae9ca1078fda92fd7c2c20411c29bc6711159e@google.com>

upspin/upspin,upspin/upspin