kbfs_ops_concur_test: disable data-race-exposing test
kbfs_ops_concur_test: disable data-race-exposing test

TestKBFSOpsTruncateAndOverwriteDeferredWithArchivedBlock exposed a
problem.  Disable while working on a fix.

Issue: KBFS-1852

keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client