Remove unnecessary displayId parameter from task creation method calls

`createFullscreenTask` and `createFreeformTask` both default to the
`DEFAULT_DISPLAY` so passing displayId 0 is redundant.

Flag: EXEMPT refactor
Test: atest WMShellUnitTests:DesktopModeCompatPolicyTest
Fix: 436189947
Change-Id: Icd344e45d0ea60ce1e58ab3edb7afbe7ebaf3e45