CHANGE: Performance improvement - removed project-wide asset migration code

[AlexTyrer]

Description

The project-wide asset migration from Input Manager asset to Input System asset was only required in 1.8.0-pre release versions. It has a small fixed cost every domain reload so we have decided to remove this code.

Changes made

Removed the project-wide asset migration code.

Testing

Usual local and automated testing.

Risk

Some old projects created during the 1.8.0-pre release may still exists. They can be converted by upgrading to 1.9.0 and then any subsequent version.

Checklist

• Changelog entry added.
  • Explains the change in Changed, Fixed, Added sections.
  • For API change contains an example snippet and/or migration example.
  • JIRA ticket linked, example (case %%). If it is a private issue, just add the case ID without a link.
  • Jira port for the next release set as "Resolved".
• Tests added/changed, if applicable.
  • Functional tests Area_CanDoX, Area_CanDoX_EvenIfYIsTheCase, Area_WhenIDoX_AndYHappens_ThisIsTheResult.
  • Performance tests.
  • Integration tests.
• Docs for new/changed API's.
  • Xmldoc cross references are set correctly.
  • Added explanation how the API works.
  • Usage code examples added.
  • The manual is updated, if needed.

During merge:

• Commit message for squash-merge is prefixed with one of the list:
  • NEW: ___.
  • FIX: ___.
  • DOCS: ___.
  • CHANGE: ___.
  • RELEASE: 1.1.0-preview.3.

After merge:

• Create forward/backward port if needed. If you are blocked from creating a forward port now please add a task to ISX-1444.

[AlexTyrer]

/ready