Remove deterministic posterior and sampler from documentation (#2410)

Summary:
## Motivation

The CI is broken after merging #2391 and #2409. It passed on the pull requests, but there may have been a Meta-internal change that never got reflected on the OSS CI, and these changes didn't wind up merged.

Pull Request resolved: #2410

Test Plan: `sphinx-build -WT --keep-going sphinx/source sphinx/build` no longer errors

Reviewed By: Balandat

Differential Revision: D59292673

Pulled By: esantorella

fbshipit-source-id: d307a8eaf37373c29ff42db75900bebb36e29b79

Author: esantorella

sphinx/source/posteriors.rst

@@ -34,11 +34,6 @@ GPyTorch Posterior
 .. automodule:: botorch.posteriors.gpytorch
     :members:
 
-Determinstic Posterior
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-.. automodule:: botorch.posteriors.deterministic
-    :members:
-
 Ensemble Posterior
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 .. automodule:: botorch.posteriors.ensemble

sphinx/source/sampling.rst

@@ -12,11 +12,6 @@ Monte-Carlo Sampler API
 .. automodule:: botorch.sampling.base
     :members:
 
-Deterministic Sampler
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-.. automodule:: botorch.sampling.deterministic
-    :members:
-
 Index Sampler
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 .. automodule:: botorch.sampling.index_sampler