Update indexmanipulations.jl (#379)

* Update indexmanipulations.jl

Remove unneeded unit op (I think?)

* Update ext/TensorKitMooncakeExt/indexmanipulations.jl

Co-authored-by: Jutho <Jutho@users.noreply.github.com>

---------

Co-authored-by: Jutho <Jutho@users.noreply.github.com>

Author: kshyatt

ext/TensorKitMooncakeExt/indexmanipulations.jl

@@ -281,10 +281,9 @@ for insertunit in (:insertleftunit, :insertrightunit)
             # sharing address spaces
             if tsrc isa TensorMap && !get(kwargs, :copy, false)
                 tsrc_cache = copy(tsrc)
-                tdst = $insertunit(tsrc, ival; kwargs...)
                 tdst_Δtdst = CoDual(
                     $insertunit(tsrc, ival; kwargs...),
-                    $insertunit(Mooncake.tangent(tsrc_Δtsrc), ival; kwargs...)
+                    $insertunit(Δtsrc, ival; kwargs...)
                 )
             else
                 tsrc_cache = nothing