fix: hard code remove GNS feature flag (#22961)

## **Description**

Hardcode `isRemoveGlobalNetworkSelectorEnabled` feature flag 

## **Changelog**

CHANGELOG entry:null

## **Related issues**

Fixes:

## **Manual testing steps**

```gherkin
Feature: my feature name

  Scenario: user [verb for user action]
    Given [describe expected initial app state]

    When user [verb for user action]
    Then [describe expected outcome]
```

## **Screenshots/Recordings**

`~`

### **Before**

`~`

### **After**

`~`

## **Pre-merge author checklist**

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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
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guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [x] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [x] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Hardcodes `isRemoveGlobalNetworkSelectorEnabled` to always return
`true`, removing the environment flag check.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
229cac5. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: vinnyhoward

app/util/networks/index.js

@@ -672,8 +672,7 @@ export const getIsNetworkOnboarded = (chainId, networkOnboardedState) =>
 export const isPermissionsSettingsV1Enabled =
   process.env.MM_PERMISSIONS_SETTINGS_V1_ENABLED === 'true';
 
-export const isRemoveGlobalNetworkSelectorEnabled = () =>
-  process.env.MM_REMOVE_GLOBAL_NETWORK_SELECTOR === 'true';
+export const isRemoveGlobalNetworkSelectorEnabled = () => true;
 
 // The whitelisted network names for the given chain IDs to prevent showing warnings on Network Settings.
 export const WHILELIST_NETWORK_NAME = {