LU-6142 tests: Remove file flock.c

LU-6142 tests: Remove file flock.c

This patch removes file lustre/tests/flock.c
This file currently is not used at all by any
tests or binary.

For flock tests validation file
lustre/tests/flocks_test.c is used instead.

Signed-off-by: Arshad Hussain <arshad.super@gmail.com>
Change-Id: Ie9b55c7a93c77234ef21a5bc7827fbaf9e9b20cd
Reviewed-on: https://review.whamcloud.com/35817
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Petros Koutoupis <pkoutoupis@cray.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>