Remove stadia from runtime asmdef (WIP)

[windxu88]

Purpose of this PR

Remove Stadia from runtime asmdef which should fall through the crack when working on ABC-393.

Ticket/Jira #: ABC-393 warning 'BuildTarget.Stadia' is obsolete: 'Stadia has been removed in 2023.1' when loading Alembic package from disk

Testing

Functional Testing status:

Performance Testing status:

Overall Product Risks

Complexity:

Halo Effect:

Documentation & UX Writing

User facing text to review		Details
User interface
Public API docs
Changelog

Documentation halo effect		Jira link
User manual
Other docs

Additional information

Note to reviewers:

Reminder:

• [ ] Add entry in CHANGELOG.md

[windxu88]

@thomas-tu , Test version 2019.4 on win job fails with following error:

Failed - "API Validation"
    Error: Removing from includePlatfoms requires a new major version. Was:"Editor, LinuxStandalone64, macOSStandalone, Stadia, WindowsStandalone64" Now:"Editor, LinuxStandalone64, macOSStandalone, WindowsStandalone64"

    The above error can be excepted with the following ValidationExceptions.json contents:
{

The error can be exempted.

However, considering this is a trival change. If we leave Stadia in the asmdef file, users won't see any difference. Maybe we give up doing this?

Note: The API validation job failures are noises, unrelated to this change.