fix: duplicate wallet started events for social login (MetaMask#27251)

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## **Description**

* `WALLET_SETUP_STARTED` and `WALLET_IMPORT_STARTED` events were firing
twice during social login.

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also include relevant motivation and context. Have in mind the following
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2. What is the improvement/solution?
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## **Related issues**

Fixes: `WALLET_SETUP_STARTED` and `WALLET_IMPORT_STARTED` events were
firing twice during social login.

## **Manual testing steps**

```gherkin
Feature: Social login wallet setup analytics

  Scenario: user starts wallet setup via Google login
    Given user is on the onboarding screen
    When user taps "Continue with Google"
    Then WALLET_SETUP_STARTED event fires once with account_type "metamask_google"
  Scenario: user starts wallet import via Apple login
    Given user is on the onboarding screen with import flow
    When user taps "Continue with Apple"
    Then WALLET_IMPORT_STARTED event fires once with account_type "imported_apple"

```

## **Screenshots/Recordings**
N/A — analytics-only change, no UI impact.
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### **Before**

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### **After**

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## **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
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Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] 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]
> **Low Risk**
> Low risk analytics-only change that moves
`WALLET_SETUP_STARTED`/`WALLET_IMPORT_STARTED` tracking to a single call
site; main risk is incorrect `account_type` attribution if the new
`getSocialAccountType` inputs are wrong.
> 
> **Overview**
> Prevents duplicate `WALLET_SETUP_STARTED` and `WALLET_IMPORT_STARTED`
metrics from firing during social login by removing the post-login
tracking in `handlePostSocialLogin` and emitting the start event once
when the social login flow begins.
> 
> Standardizes the `account_type` property for these start events by
deriving it via `getSocialAccountType(provider, !createWallet)` instead
of manual string formatting.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
43388b0. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: grvgoel81

app/components/Views/Onboarding/index.tsx

@@ -416,16 +416,6 @@ const Onboarding = () => {
         const accountType = getSocialAccountType(provider, result.existingUser);
         dispatch(setAccountType(accountType));
 
-        if (result.existingUser) {
-          track(MetaMetricsEvents.WALLET_IMPORT_STARTED, {
-            account_type: accountType,
-          });
-        } else {
-          track(MetaMetricsEvents.WALLET_SETUP_STARTED, {
-            account_type: accountType,
-          });
-        }
-
         track(MetaMetricsEvents.SOCIAL_LOGIN_COMPLETED, {
           account_type: accountType,
         });
@@ -700,13 +690,14 @@ const Onboarding = () => {
         tags: getTraceTags(store.getState()),
       });
 
+      const accountType = getSocialAccountType(provider, !createWallet);
       if (createWallet) {
         track(MetaMetricsEvents.WALLET_SETUP_STARTED, {
-          account_type: `${AccountType.Metamask}_${provider}`,
+          account_type: accountType,
         });
       } else {
         track(MetaMetricsEvents.WALLET_IMPORT_STARTED, {
-          account_type: `${AccountType.Imported}_${provider}`,
+          account_type: accountType,
         });
       }