Remove outdated logic of task reparent

The logic was used for 2 level task PiP. Since PiP task becomes
one level task for years, these are dead code.

Bug: 163976519
Flag: EXEMPT remove dead code
Test: CtsWindowManagerDeviceActivity
Change-Id: I4c52d122f4e9488bf4a5ba743323ad5a9f251aa3
1 file changed