qa/suites/crimson-rados/thrash_simple: enable osd down

Signed-off-by: Xuehan Xu <[email protected]>

Author: xxhdx1985126

qa/suites/crimson-rados/thrash_simple/thrashers/simple.yaml

@@ -25,7 +25,6 @@ tasks:
     sighup_delay: 0
     min_in: 3
     noscrub_toggle_delay: 0
-    chance_down: 0
     chance_thrash_pg_upmap: 0
     reweight_osd: 0
     thrash_primary_affinity: false