Remove outdated workaround

Author: mhauru

ext/DynamicPPLChainRulesCoreExt.jl

@@ -25,9 +25,5 @@ ChainRulesCore.@non_differentiable DynamicPPL.updategid!(
 ChainRulesCore.@non_differentiable DynamicPPL.infer_nested_eltype(x)
 
 ChainRulesCore.@non_differentiable DynamicPPL.recontiguify_ranges!(ranges)
-# TODO(mhauru) A workaround for https://github.com/FluxML/Zygote.jl/issues/1523, remove when
-# fixed. Note that this is some serious type piracy. Needed because VarNamedVector uses
-# BitVectors.
-ChainRulesCore.@non_differentiable BitVector(a, b)
 
 end # module