Remove the check of Transitions.ENABLE_SHELL_TRANSITIONS for desktop mode...

Remove the check of Transitions.ENABLE_SHELL_TRANSITIONS for desktop mode use-cases since the flag value is default true.

This is to simplify the code and avoid refactoring code that is obsolete.

Bug: 332682201
Flag: EXEMPT (no changes needed)
Change-Id: Idb0c8a395bc3537a3708199b7f5d2676953e77d3