Remove mapPartial from mllist

It seems that mllist redefines mapPartial which already exists in list:

listTheory.mapPartial_def;
val it =
   ⊢ (∀f. mapPartial f [] = []) ∧
     ∀f x xs.
       mapPartial f (x::xs) =
       case f x of NONE => mapPartial f xs | SOME y => y::mapPartial f xs:
   thm
> mllistTheory.mapPartial_def;
val it =
   ⊢ (∀f. mapPartial f [] = []) ∧
     ∀f h t.
       mapPartial f (h::t) =
       case f h of NONE => mapPartial f t | SOME x => x::mapPartial f t: thm

I ran into this issue after spending some time not understanding why mapPartial_def is not doing anything as I had an mllist as my ancestors.

I suspect the fix is basically as simple as just deleting the definition, with perhaps minor changes required here and there.