Remove TS item on setting cinder simple scheduler

The Chance and Simple schedulers of cinder are now deprecated, setting
them will just default to the Filter scheduler anyway. This patch
deletes a Troubleshooting section advising users to set the Simple
scheduler (specifically,
doc/admin-guide-cloud/section_ts_failed_sched_create_vol.xml).

Partially implements bp: deprecate-chance-and-simple-schedulers

Change-Id: I1155358c6c11c54432d720a2eca78b6fe3174951
Merge "Remove TS item on setting cinder simple scheduler"