mk: removeo-allo — remove every occurrence

Three conde clauses: empty list -> empty result; head matches x ->
skip and recurse; head differs (nafc-gated) -> keep and recurse.
Distinct from rembero, which removes only the first occurrence.

5 new tests, 446/446 cumulative.

lib/minikanren/relations.sx

@@ -148,6 +148,15 @@
       ((fresh (a d) (conso a d l) (== a x) (== out d)))
       ((fresh (a d res) (conso a d l) (nafc (== a x)) (conso a res out) (rembero x d res))))))
 
+(define
+  removeo-allo
+  (fn
+    (x l result)
+    (conde
+      ((nullo l) (nullo result))
+      ((fresh (a d) (conso a d l) (== a x) (removeo-allo x d result)))
+      ((fresh (a d r-rest) (conso a d l) (nafc (== a x)) (conso a r-rest result) (removeo-allo x d r-rest))))))
+
 (define
   assoco
   (fn