[GRAPHX] Remove unused variables left over by previous refactoring.

## What changes were proposed in this pull request?

Some variables were previously used for indexing the routing table's backing
array, but that indexing now happens elsewhere, and so the variables aren't needed.

## How was this patch tested?

Unit tests.

(This contribution is my original work and I license the work to Spark under its open source license.)

Closes apache#23112 from huonw/remove-unused-variables.

Authored-by: Huon Wilson <[email protected]>
Signed-off-by: Sean Owen <[email protected]>

Author: huonw

graphx/src/main/scala/org/apache/spark/graphx/impl/ShippableVertexPartition.scala

@@ -117,13 +117,11 @@ class ShippableVertexPartition[VD: ClassTag](
       val initialSize = if (shipSrc && shipDst) routingTable.partitionSize(pid) else 64
       val vids = new PrimitiveVector[VertexId](initialSize)
       val attrs = new PrimitiveVector[VD](initialSize)
-      var i = 0
       routingTable.foreachWithinEdgePartition(pid, shipSrc, shipDst) { vid =>
         if (isDefined(vid)) {
           vids += vid
           attrs += this(vid)
         }
-        i += 1
       }
       (pid, new VertexAttributeBlock(vids.trim().array, attrs.trim().array))
     }
@@ -137,12 +135,10 @@ class ShippableVertexPartition[VD: ClassTag](
   def shipVertexIds(): Iterator[(PartitionID, Array[VertexId])] = {
     Iterator.tabulate(routingTable.numEdgePartitions) { pid =>
       val vids = new PrimitiveVector[VertexId](routingTable.partitionSize(pid))
-      var i = 0
       routingTable.foreachWithinEdgePartition(pid, true, true) { vid =>
         if (isDefined(vid)) {
           vids += vid
         }
-        i += 1
       }
       (pid, vids.trim().array)
     }