libafs: remove stray "-v 2" argument to afs_compile_et

Commit 4e6b7ab904d38d38da1b80a7342bd815668a8c09 separated the
compile_et rules for creating the source and header files using
the new -emit functionality. During review for inclusion in 1.6,
Chas Williams spotted a stray "-v 2" carried over to the rule
for creating the header file, where it doesn't apply. Remove it.

Change-Id: I554354eae0fa018e56fe7b78df69a43e5b5a0b07
Reviewed-on: http://gerrit.openafs.org/11347
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: D Brashear <shadow@your-file-system.com>