Add desk removal APIs to `IDesktopMode`.

Add the API needed to remove a desk given its ID as well as
all the desks on all displays.

BUG: 390715986
Test: m
Flag: com.android.window.flags.enable_multiple_desktops_frontend
Flag: com.android.window.flags.enable_multiple_desktops_backend
Change-Id: Ifd4180ca5890fc04b5904ac44c6ebcd2ebe22973