`RepeatSampler` should be in AbstractMCMC

[penelopeysm]

It has very little to do with Turing, it's just a thin wrapper around another sampler. I am fairly sure it should go into AbstractMCMC (or a package that depends only on AbstractMCMC) and the only thing that needs to be kept here are these two methods:

Turing.jl/src/mcmc/repeat_sampler.jl

Lines 27 to 33 in 296f654

	function RepeatSampler(alg::InferenceAlgorithm, num_repeat::Int)
	return RepeatSampler(Sampler(alg), num_repeat)
	end
	function setparams_varinfo!!(model::DynamicPPL.Model, sampler::RepeatSampler, state, params)
	return setparams_varinfo!!(model, sampler.sampler, state, params)
	end

although if we remove DynamicPPL.Sampler (TuringLang/DynamicPPL.jl#1037) then even the first one can go too.