Remove the validation check when enter split

Remove the validation checking first before we fix the PiP-to-Split
case. The validation checking is to prevent entering the unexpected
state in split when launched by adb with activity_adjacent flag.
2369dfab, e9c7b90a, already fixed it from wm-core.
We can do the validation checking from split after.

Bug: 240652871
Test: 1. Launch app from recent app.
      2. Drag app to split from task bar.
Change-Id: Ia61f91dd2d505cc8b0d4f8194798b16222253ce4