LU-14832 llite: Correct cl_env comments

LU-14832 llite: Correct cl_env comments

The comments related to cl_env caching behavior are
dangerously out of date and misleading, describing an
old caching mechanism which was linked to threads.

This has not been present for some time, and we cannot use
cl_env_get to get the environment for a thread as it
describes.

Correct the various comments and remove a now extraneous
include.

Test-Parameters: trivial
Fixes: 4533271278 ("LU-4257 obdclass: Get rid of cl_env hash table")
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I0a855094c66281bfb35e234ecad1af3b923e8538
Reviewed-on: https://review.whamcloud.com/44191
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Wang Shilong <wangshilong1991@gmail.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>