EX-5909 tests: clean up in sanity-quota/16a

EX-5909 tests: clean up in sanity-quota/16a

Clean up the test file in sanity-quota test_16a.  If test_16b is
run (DNE config) then the filesystem is reformatted, but in the
non-DNE config test_17 will fail if there is used quota.

Test-Parameters: trivial testlist=sanity-quota
Fixes: b54b7ce43929 ("LU-14472 quota: skip non-exist or inact tgt for lfs_quota")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Id1faeab9df246d8010bf114582ab17a75846db68
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/48899
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>