Replace old Gibbs sampler with the experimental one.

Author: mhauru

src/Turing.jl

@@ -86,7 +86,6 @@ export @model,                 # modelling
     Emcee,
     ESS,
     Gibbs,
-    GibbsConditional,
     HMC,                    # Hamiltonian-like sampling
     SGLD,
     SGHMC,