[7.0] Remove CMSObject and LegacyPropertyManagementTrait

[Hackwar]

• I read the Generative AI policy and my contribution is either not created with the help of AI or is compatible with the policy and GNU/GPL 2 or later.

Summary of Changes

This PR removes the CMSObject class and the LegacyPropertyManagementTrait and all remaining remnants from the core. This code has been deprecated for literally decades already. The PR depends on the following PRs

• [7.0] Changelog: Removing LegacyPropertyManagementTrait #44897
• [7.0] Remove LegacyPropertyManagementTrait from CategoryNode #44904
• [7.0] Remove LegacyPropertyManagementTrait from MVC classes #44907
• [7.0] Remove usage of LegacyPropertyManagementTrait from Table class #44909
• [7.0] Remove LegacyPropertyManagementTrait from User class #44906

Testing Instructions

Codereview

Link to documentations

Please select:

• Documentation link for guide.joomla.org:

• No documentation changes for guide.joomla.org needed

• Pull Request link for manual.joomla.org: Removal of LegacyPropertyManagementTrait and CMSObject Manual#615

• No documentation changes for manual.joomla.org needed

[laoneo]

I would move the CMSObject class and the LegacyPropertyManagementTrait to the compat plugin first. Directly removing it will definitely cause a lot of trouble in 3rd party extension.