iOS - remove PIN entry from Keychain on fresh install

[bsclifton]

Description:

There is a situation that users can get into where they can forget their PIN. On iOS, there isn't a way to go and edit the keychain so after uninstalling/reinstalling they'll get hit with the same code and can't open Brave

Steps to Reproduce

1. Install Brave
2. Setup a PIN code
3. Forget what PIN code is
4. Uninstall Brave
5. Reinstall Brave

Actual result:
User is met with PIN again ☹️ See for more info:
https://community.brave.com/t/forgot-brave-ios-app-passcode/236334

Expected result:
Removing/reinstalling should clear the keychain entry and allow Brave to be used again

[srirambv]

Verification passed on iPhone XR with iOS 13.5 running 1.26(21.5.26.21)

• Verified test plan from Fix #3598: Initialize DB after store existence check for passcode reset #3619
• Verified no pin prompt when app is uninstalled and reinstalled

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Verification passed on iPhone 7+ with iOS 14.5.1 running 1.26(21.5.26.21)

• Verified test plan from Fix #3598: Initialize DB after store existence check for passcode reset #3619
• Verified no pin prompt when app is uninstalled and reinstalled

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Verification passed on iPad Pro with iOS 14.5.1 running 1.26(21.5.26.21)

• Verified test plan from Fix #3598: Initialize DB after store existence check for passcode reset #3619
• Verified no pin prompt when app is uninstalled and reinstalled