LU-17038 tests: remove munlink utility

LU-17038 tests: remove munlink utility

The munlink utility is obsoleted by the unlink command added in
the coreutils package many moons ago, and can be removed.  All
tests using munlink are replaced with unlink.

Test-Parameters: trivial testlist=recovery-small,replay-dual,replay-single
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I984406525ed958814bd8af74a2d81c4920e320b0
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51977
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>