fix: remove duplicate sign-in calls

[mathieuartu]

Description

This PR ensures that the sign-in process happen only at the "pin extension" screen during onboarding.
It was previously also called at the "creation successful" screen, but this is not needed since onboarding always ends with the "pin extension" screen.

It also removes the useCreateSession hook, as this is not needed anymore since we directly call performSignIn from the background.

Related issues

Fixes: https://consensyssoftware.atlassian.net/browse/IDENTITY-9

Manual testing steps

1. Do a fresh install
2. Open your network tab and filter with "login"
3. Do an onboarding and verify that this is called only once

Screenshots/Recordings

Before

After

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). 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.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[metamaskbot]

Builds ready [918daf6]

• builds: chrome, firefox
• builds (flask): chrome, firefox
• builds (MMI): chrome
• builds (test): chrome, firefox
• builds (test-flask): chrome, firefox
• build viz: Build System
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5, 6, 7
  • common: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13
  • ui: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13
  • content-script: 0
  • offscreen: 0

Page Load Metrics (1567 ± 30 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	1454	1703	1568	64	31
		domContentLoaded	1442	1696	1547	62	30
		load	1456	1704	1567	63	30
		domInteractive	24	119	40	27	13
		backgroundConnect	8	52	25	15	7
		firstReactRender	16	76	41	25	12
		getState	4	60	11	14	7
		initialActions	0	0	0	0	0
		loadScripts	1021	1296	1107	65	31
		setupStore	7	48	13	11	5
		uiStartup	1643	2011	1785	83	40

Bundle size diffs

• background: 0 Bytes (0.00%)
• ui: -1.72 KiB (-0.02%)
• common: 0 Bytes (0.00%)