fix: use pairingTopic for permission revocation in removeSession() (MetaMask#27945)

## Description

`removeSession()` calls
`permissionsController.revokeAllPermissions(session.topic)`, but
permissions are stored under `session.pairingTopic` (used as `channelId`
/ `origin` when `requestPermissions` is called in
`_handleSessionProposal` — lines 468, 581).

Since `topic` and `pairingTopic` are always different values, the
revocation was targeting a non-existent subject and silently failing
(caught by the surrounding try/catch). Stale permission entries
accumulated in the `PermissionController` for every disconnected WC
session.

This changes the revocation key to `session.pairingTopic` to match how
permissions are created.

## Related issues

Fixes: https://consensyssoftware.atlassian.net/browse/WAPI-1361


## **Changelog**

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CHANGELOG entry: Fixed - Fixed removeSession() using session.topic
instead of session.pairingTopic when revoking WalletConnect permissions,
which caused stale permission entries to persist in the
PermissionController
([MetaMask#27945](MetaMask#27945))

## Manual testing steps

1. Connect a dapp via WalletConnect
2. Inspect `PermissionController.state.subjects` — the dapp's entry
should be keyed by `pairingTopic`
3. Disconnect the session (long-press in Settings > Experimental > WC
Sessions)
4. Inspect `PermissionController.state.subjects` — the entry should now
be removed

## Pre-merge author checklist

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I've included tests if applicable
- [x] I've documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I've applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Changes how WalletConnect v2 session teardown revokes permissions,
which impacts permission state cleanup and could affect disconnect
behavior if the wrong identifier is used elsewhere. Scope is small and
covered by an updated unit test.
> 
> **Overview**
> Fixes `WC2Manager.removeSession()` to revoke permissions using
`session.pairingTopic` (and logs that identifier) instead of
`session.topic`, preventing stale `PermissionController` subjects from
accumulating after disconnects.
> 
> Updates the `WalletConnectV2` unit test to assert
`revokeAllPermissions` is called with the pairing topic.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
8ba16c9. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: adonesky1

app/core/WalletConnect/WalletConnectV2.test.ts

@@ -864,7 +864,7 @@ describe('WC2Manager', () => {
         },
         topic: 'test-topic',
       });
-      expect(revokeAllPermissionsSpy).toHaveBeenCalledWith('test-topic');
+      expect(revokeAllPermissionsSpy).toHaveBeenCalledWith('test-pairing');
     });
   });
 

app/core/WalletConnect/WalletConnectV2.ts

@@ -381,10 +381,10 @@ export class WC2Manager {
         }
       ).PermissionController;
       DevLogger.log(
-        `WC2::removeSession revokeAllPermissions for ${session.topic}`,
+        `WC2::removeSession revokeAllPermissions for ${session.pairingTopic}`,
         permissionsController.state,
       );
-      permissionsController.revokeAllPermissions(session.topic);
+      permissionsController.revokeAllPermissions(session.pairingTopic);
     } catch (err) {
       DevLogger.log(`WC2::removeSession error while disconnecting`, err);
     }