[util] address TODO to remove dummy encryption key

I noticed compiler's warning on unused variable and realized it's time
to address corresponding TODO in util/env_posix.cc.

This patch doesn't contain any functional modifications.

Change-Id: I09be400428b83fb3f5c8494df54f271bb4b0b33c
Reviewed-on: http://gerrit.cloudera.org:8080/18904
Tested-by: Kudu Jenkins
Reviewed-by: Yingchun Lai <acelyc1112009@gmail.com>
Reviewed-by: Attila Bukor <abukor@apache.org>
1 file changed