Remove optimized combineAll

Author: Luka Jacobowitz

core/src/main/scala/cats/instances/sortedMap.scala

@@ -6,7 +6,6 @@ import cats.kernel.instances.StaticMethods
 
 import scala.annotation.tailrec
 import scala.collection.immutable.SortedMap
-import scala.collection.mutable
 
 trait SortedMapInstances extends SortedMapInstances1 {
 
@@ -159,15 +158,4 @@ class SortedMapMonoid[K, V](implicit V: Semigroup[V], O: Order[K]) extends Monoi
       }
     }
 
-  override def combineAll(xss: TraversableOnce[SortedMap[K, V]]): SortedMap[K, V] = {
-    val acc = mutable.SortedMap.empty[K, V](O.toOrdering)
-    xss.foreach { m =>
-      val it = m.iterator
-      while (it.hasNext) {
-        val (k, v) = it.next
-        acc(k) = Semigroup.maybeCombine(acc.get(k), v)
-      }
-    }
-    SortedMap.empty[K, V](O.toOrdering) ++ acc
-  }
 }