remove duplicate function definitions

Author: Maximilian-Stefan-Ernst

src/frontend/specification/documentation.jl

@@ -1,37 +1,3 @@
-param_labels(spec::SemSpecification) = spec.param_labels
-
-"""
-    vars(semobj) -> Vector{Symbol}
-
-Return the vector of SEM model variables (both observed and latent)
-in the order specified by the model.
-"""
-function vars end
-
-vars(spec::SemSpecification) = error("vars(spec::$(typeof(spec))) is not implemented")
-
-"""
-    observed_vars(semobj) -> Vector{Symbol}
-
-Return the vector of SEM model observed variable in the order specified by the
-model, which also should match the order of variables in [`SemObserved`](@ref).
-"""
-function observed_vars end
-
-observed_vars(spec::SemSpecification) =
-    error("observed_vars(spec::$(typeof(spec))) is not implemented")
-
-"""
-    latent_vars(semobj) -> Vector{Symbol}
-
-Return the vector of SEM model latent variable in the order specified by the
-model.
-"""
-function latent_vars end
-
-latent_vars(spec::SemSpecification) =
-    error("latent_vars(spec::$(typeof(spec))) is not implemented")
-
 """
     vars(semobj) -> Vector{Symbol}