Remove another literal_getproperty(sol, ::Val{:u}) dispatch

[DhairyaLGandhi]

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

This is in continuation from #1193. Here, the return type for some common operations might change, so this might be considered breaking

Zygote.gradient(sol) do sol
    o = reduce(hcat, state_values(sol))
    sum(o)
end

Zygote.gradient(sol) do sol
    o = reduce(hcat, sol.u)
    sum(o)
end

etc go from returning solution types to Tangent types instead

Add any other context about the problem here.

[DhairyaLGandhi]

One of the errors is SciML/SciMLBase.jl#1020