LU-15815 llite: disable fast_read and workaround

LU-15815 llite: disable fast_read and workaround

Revert the fast_read stale data workaround from LU-14541 and disable
fast_read by default. The workaround causes applications to receive
spurious SIGBUGs when reclaim is concurrent with mmap page fault
handlers. We disable fast read to avoid the stale data issue entirely.

This reverts commit f2a16793fa4316fc9ccdc46bcfe54f6b8d1e442b and
re-exposes us to the consistency issues described in LU-14541.

Lustre-change: https://review.whamcloud.com/47204

Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: I716b1fd6ab22242b9267b8883f0371a360aaecef
Reviewed-on: https://review.whamcloud.com/47205
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>