ubik: Remove bare global ubik_epochTime

Commit e4ac552a moved ubik_epochTime into a global version_globals
struct. However, it missed a references to the existing
ubik_epochTime value it was moving, as well as its declaration. Remove
the declaration, and move the reference to use the version_globals
structure.

Change-Id: I2552ba850f286b2b93f3c1b696d993a7cfc074c8
Reviewed-on: http://gerrit.openafs.org/8918
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>