Update tutorials to work with Posterior & MCSampler refactor (#1506)

Summary:
Pull Request resolved: #1506

See title. Also deletes the empty files leftover by the refactor.

Reviewed By: dme65

Differential Revision: D41366067

fbshipit-source-id: 1dbce5271b5ed1813f942134782315c1deda3127

Author: saitcakmak

botorch/sampling/samplers.py

@@ -41,8 +41,3 @@ Stochastic Samplers
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 .. automodule:: botorch.sampling.stochastic_samplers
     :members:
-
-Deprecated
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-.. automodule:: botorch.sampling.samplers
-    :members: