LU-16518 mdt: fix unused-but-set-variable warnings

LU-16518 mdt: fix unused-but-set-variable warnings

Remove unused variables in various parts of the MDT code.
This silences the Clang compiler -Wunused-but-set-variable
warning.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I2c42e9ce86ac854a49f8b12f5325ce1f34b8ecc3
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58184
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Max Wang <wamax@amazon.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>