LU-18813 osd-wbcfs: remove f_op llseek checks

LU-18813 osd-wbcfs: remove f_op llseek checks

MemFS will always have llseek defined, so we
can remove the checks in the OSD.

Test-Parameters: trivial
Test-Parameters: testlist=sanity fstype=wbcfs mdscount=4 mdtcount=1 osscount=4 ostcount=1
Test-Parameters: testlist=sanity fstype=wbcfs combinedmdsmgs=false standalonemgs=true mdscount=1 mdtcount=1 osscount=4 ostcount=1
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I77f7abcef686c9c654b7bee04b3f88bb89a87756
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/59305
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Qian Yingjin <qian@ddn.com>
Reviewed-by: Lijing Chen <lijinc@amazon.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>