refactor: remove old `==` and `hash` implementation for `System`#3683

ChrisRackauckas merged 2 commits intoSciML:masterSciML/ModelingToolkit.jl:masterfrom

AayushSabharwal:as/rm-isequal-hashAayushSabharwal/ModelingToolkit.jl:as/rm-isequal-hashCopy head branch name to clipboard