Remove stray underscore from preprocessor conditional

Remove stray underscore from preprocessor conditional

AFS_FBSD_110_ENV is not defined anywhere, so this conditional
did not behave as expected.

Introduced by me in commit e51d3b13c2b208efe72b584b532a28444633feff
which was apparently not as well tested as it could have been.

Change-Id: I57da8f69ba963b7602092bc524c6435059d8ae12
Reviewed-on: http://gerrit.openafs.org/11944
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams <3chas3@gmail.com>
Reviewed-by: Perry Ruiter <pruiter@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>