Outdated comments in source code

[hochB]

I found 2 outdated comments in the source code.

https://github.com/JuliaOpt/JuMP.jl/blob/master/src/JuMP.jl#L622
Fixed: JuliaLang/julia#29878

https://github.com/JuliaOpt/JuMP.jl/blob/master/src/copy.jl#L106
Fixed: jump-dev/MathOptInterface.jl#495