Remove unused background API methods (#12731)

These background API methods were not used anywhere in the UI. One of
them was called in `actions.js` by a function that itself was never
called, so it have been removed. Additionally, one unused `actions.js`
function was found and removed as well.

`setAdvancedGasFee` is the only unused background method that remains.
It was recently added and will be used in the near future.

app/scripts/metamask-controller.js

@@ -1008,9 +1008,7 @@ export default class MetamaskController extends EventEmitter {
       ),
       createCancelTransaction: nodeify(this.createCancelTransaction, this),
       createSpeedUpTransaction: nodeify(this.createSpeedUpTransaction, this),
-      isNonceTaken: nodeify(txController.isNonceTaken, txController),
       estimateGas: nodeify(this.estimateGas, this),
-      getPendingNonce: nodeify(this.getPendingNonce, this),
       getNextNonce: nodeify(this.getNextNonce, this),
       addUnapprovedTransaction: nodeify(
         txController.addUnapprovedTransaction,
@@ -1094,13 +1092,6 @@ export default class MetamaskController extends EventEmitter {
         permissionsController.approvePermissionsRequest,
         permissionsController,
       ),
-      clearPermissions: permissionsController.clearPermissions.bind(
-        permissionsController,
-      ),
-      getApprovedAccounts: nodeify(
-        permissionsController.getAccounts,
-        permissionsController,
-      ),
       rejectPermissionsRequest: nodeify(
         permissionsController.rejectPermissionsRequest,
         permissionsController,

ui/store/actions.js

@@ -1356,12 +1356,6 @@ export function acceptWatchAsset(suggestedAssetID) {
   };
 }
 
-export function addKnownMethodData(fourBytePrefix, methodData) {
-  return () => {
-    background.addKnownMethodData(fourBytePrefix, methodData);
-  };
-}
-
 export function clearPendingTokens() {
   return {
     type: actionConstants.CLEAR_PENDING_TOKENS,
@@ -2403,19 +2397,6 @@ export function removePermissionsFor(domains) {
   };
 }
 
-/**
- * Clears all permissions for all domains.
- */
-export function clearPermissions() {
-  return (dispatch) => {
-    background.clearPermissions((err) => {
-      if (err) {
-        dispatch(displayWarning(err.message));
-      }
-    });
-  };
-}
-
 // Pending Approvals
 
 /**