Remove special iszero handling

Author: avik-pal

src/levenberg.jl

@@ -185,7 +185,7 @@ end
 
 function perform_step!(cache::LevenbergMarquardtCache{true})
     @unpack fu1, f, make_new_J = cache
-    if _iszero(fu1)
+    if iszero(fu1)
         cache.force_stop = true
         return nothing
     end
@@ -256,7 +256,7 @@ end
 
 function perform_step!(cache::LevenbergMarquardtCache{false})
     @unpack fu1, f, make_new_J = cache
-    if _iszero(fu1)
+    if iszero(fu1)
         cache.force_stop = true
         return nothing
     end

src/utils.jl

@@ -129,10 +129,6 @@ end
 concrete_jac(_) = nothing
 concrete_jac(::AbstractNewtonAlgorithm{CJ}) where {CJ} = CJ
 
-# Circumventing https://github.com/SciML/RecursiveArrayTools.jl/issues/277
-_iszero(x) = iszero(x)
-_iszero(x::ArrayPartition) = all(_iszero, x.x)
-
 _mutable_zero(x) = zero(x)
 _mutable_zero(x::SArray) = MArray(x)