Backport "Don't updatePendingTxs outside of block updates (#8445)" (#8474)

Backport #8445 to v7.7.9. Original commit description:

* Don't updatePendingTxs outside of block updates

Refs #8377

Reverts 507397f6c (#5431)

* Check for new block data on unlock

Co-authored-by: Whymarrh Whitby <whymarrh.whitby@gmail.com>

app/scripts/controllers/transactions/index.js

@@ -724,7 +724,6 @@ class TransactionController extends EventEmitter {
     Updates the memStore in transaction controller
   */
   _updateMemstore () {
-    this.pendingTxTracker.updatePendingTxs()
     const unapprovedTxs = this.txStateManager.getUnapprovedTxList()
     const selectedAddressTxList = this.txStateManager.getFilteredTxList({
       from: this.getSelectedAddress(),

app/scripts/metamask-controller.js

@@ -767,7 +767,7 @@ module.exports = class MetamaskController extends EventEmitter {
     }
 
     await this.preferencesController.syncAddresses(accounts)
-    await this.txController.pendingTxTracker.updatePendingTxs()
+    await this.blockTracker.checkForLatestBlock()
 
     try {
       const threeBoxSyncingAllowed = this.threeBoxController.getThreeBoxSyncingState()