simplify StructArrays handling

can just rely on the ConstructionBase support there

ext/AccessorsStructArraysExt.jl

@@ -11,19 +11,6 @@ Accessors.delete(x::StructArray{<:Union{Tuple, NamedTuple}}, o::PropertyLens) =
 
 Accessors.set(x::StructArray{<:Union{Tuple, NamedTuple}}, ::typeof(propertynames), names) = set(x, propertynames ∘ StructArrays.components, names)
 
-# (named)tuple eltypes: only component arrays themselves are needed in the constructor
-# can change component number/names
-Accessors.set(x::StructArray{<:Union{Tuple, NamedTuple}}, ::typeof(StructArrays.components), v) = StructArray(v)
+Accessors.set(x::StructArray, ::typeof(StructArrays.components), v) = constructorof(typeof(x))(v)
 
-# other eltypes: need to pass eltype to the constructor in addition to component arrays
-# component number/names stay the same
-function Accessors.set(x::StructArray{T}, ::typeof(StructArrays.components), v::VT) where {T, VT}
-    # resulting eltype is basically T, but potentially with different type parameters
-    # probe its constructorof to get the right concrete type
-    ET = Base.promote_op(constructorof(T), map(eltype, _eltypes(VT))...)
-    StructArray{ET}(v)
-end
-
-_eltypes(::Type{T}) where {T <: Tuple} = Tuple(T.parameters)
-_eltypes(::Type{NamedTuple{K, T}}) where {K, T <: Tuple} = Tuple(T.parameters)
 end