[VPlan] Remove unneeded code connecting blocks in VPBB:splitAt (NFC).

insertBlockAfter already takes care of transferring successors. Remove
unneeded code to transfer them manually.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -552,18 +552,10 @@ VPBasicBlock *VPBasicBlock::splitAt(iterator SplitAt) {
          "can only split at a position in the same block");
 
   SmallVector<VPBlockBase *, 2> Succs(successors());
-  // First, disconnect the current block from its successors.
-  for (VPBlockBase *Succ : Succs)
-    VPBlockUtils::disconnectBlocks(this, Succ);
-
   // Create new empty block after the block to split.
   auto *SplitBlock = new VPBasicBlock(getName() + ".split");
   VPBlockUtils::insertBlockAfter(SplitBlock, this);
 
-  // Add successors for block to split to new block.
-  for (VPBlockBase *Succ : Succs)
-    VPBlockUtils::connectBlocks(SplitBlock, Succ);
-
   // Finally, move the recipes starting at SplitAt to new block.
   for (VPRecipeBase &ToMove :
        make_early_inc_range(make_range(SplitAt, this->end())))