Refactor FXIOS-7596 [v121] remove legacy store (backport #17224)

[mergify]

This is an automatic backport of pull request #17224 done by Mergify.
Cherry-pick of 21d5c81 has failed:

On branch mergify/bp/release/v121/pr-17224
Your branch is up to date with 'origin/release/v121'.

You are currently cherry-picking commit 21d5c818e.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
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Changes to be committed:
	modified:   Client/Application/UITestAppDelegate.swift
	modified:   Client/Frontend/Browser/BrowserViewController/BrowserViewController+TabToolbarDelegate.swift
	modified:   Client/Frontend/Browser/Tabs/Legacy/LegacyGridTabViewController.swift
	modified:   Client/Frontend/Browser/Tabs/Legacy/LegacyTabTrayViewController.swift
	deleted:    Client/TabManagement/Legacy/LegacySavedTab+ConfigureExtension.swift
	modified:   Client/TabManagement/Legacy/LegacyTabManager.swift
	deleted:    Client/TabManagement/Legacy/LegacyTabManagerStore.swift
	modified:   Client/TabManagement/TabManagerImplementation.swift

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   Client.xcodeproj/project.pbxproj

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[mobiletest-ci-bot]

	Messages
📖	Project coverage: 33.7%
📖	Edited 7 files
📖	Created 0 files

Client.app: Coverage: 32.3

File	Coverage
LegacyTabManager.swift	25.83%	⚠️
LegacyTabTrayViewController.swift	41.93%	⚠️
TabManagerImplementation.swift	49.39%	⚠️
UITestAppDelegate.swift	0.0%	⚠️
BrowserViewController+TabToolbarDelegate.swift	11.03%	⚠️
LegacyGridTabViewController.swift	31.4%	⚠️

Generated by 🚫 Danger Swift against 26dc5e4