removing OPM diff page and adding redirect

Author: sbvegan

pages/chain/differences.mdx

@@ -103,4 +103,5 @@
 /stack/operators/features/op-txproxy /builders/chain-operators/tools/op-txproxy
 /stack/operators/features/proxyd /builders/chain-operators/tools/proxyd
 /builders/notices/granite-changes https://github.com/ethereum-optimism/docs/blob/ef619668ae44276edecdfd657157254b9809e2d6/pages/builders/notices/granite-changes.mdx
-/builders/notices/fp-changes https://github.com/ethereum-optimism/docs/blob/ef619668ae44276edecdfd657157254b9809e2d6/pages/builders/notices/fp-changes.mdx
+/builders/notices/fp-changes https://github.com/ethereum-optimism/docs/blob/ef619668ae44276edecdfd657157254b9809e2d6/pages/builders/notices/fp-changes.mdx
+/chain/differences /stack/differences