Refactor FXIOS-9085 #20125 Remove legacy inactive tab code

:scroll: Tickets

Remove remaining legacy inactive tab code. This part was a little more tangled up with small things here and there:

AppSessionProvider didn't need tabUpdateState anymore as this related only to the legacy Inactive Tabs feature
Inactive tabs were entirely removed from the LegacyTabDisplayManager as this class is only used now for top tabs. This means TabDisplayType.TabGrid can be removed as only TabDisplayType.TopTabTray will ever be used in the application.

I will do a follow up PR to rename LegacyTabDisplayManager to TopTabDisplayManager for clarity I think.

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[X] Filled in the above information (tickets numbers and description of your work)
[X] Updated the PR name to follow our PR naming guidelines
[X] Wrote unit tests and/or ensured the tests suite is passing
[ ] When working on UI, I checked and implemented accessibility (minimum Dynamic Text and VoiceOver)
[ ] If needed, I updated documentation / comments for complex code and public methods
[ ] If needed, added a backport comment (example @Mergifyio backport release/v120)

File	Coverage
TopTabsViewController.swift	0.0%	⚠️
AppSessionManager.swift	100.0%	✅
TabDisplayManager.swift	0.0%	⚠️
TabManager.swift	62.5%	✅
ToggleInactiveTabs.swift	0.0%	⚠️
LegacyTabManager.swift	35.34%	⚠️