Delete Class::zGetSProp.

Summary: It only had one callsite, inside of EZC. Inline that callsite and add an assert
that the returned sprop is not Uninit.

Reviewed By: @paulbiss

Differential Revision: D1742950

Signature: t1:1742950:1418759196:fb6f9218614904c59e1fd2fdc3d864321a89fdd9
Move verbose setting into benchy_config

Summary: Verbosity applies across all of the benchy scripts, so move it
into a central place so that it works correctly.

Reviewed By: @jdelong

Differential Revision: D1740138

Signature: t1:1740138:1418758374:ae750b3d59f76cd04d7d95964e44ad01f389b96a