fix docs additions

Author: ferrine

docs/api_reference.rst

@@ -30,22 +30,11 @@ Distributions
 
    GenExtreme
    GeneralizedPoisson
-   histogram_utils.histogram_approximation
    DiscreteMarkovChain
    R2D2M2CP
    histogram_approximation
 
 
-Gaussian Processess
-===================
-
-.. currentmodule:: pymc_experimental.gp
-.. autosummary::
-   :toctree: generated/
-
-   latent_approx.HSGP
-
-
 Utils
 =====