Remove InputMonitor.pilferPointers API from Shell

This API is deprecated and should be removed.
The proper API is InputManager::pilferPointers.

This will also eventually allow us to properly handle InputChannel
lifecycle, and also will reduce the work needed to switch away from
InputMonitor completely.

Bug: 323450804
Test: presubmit
Flag: EXEMPT refactor
Change-Id: I529b44fc509319487df0f6a24ee1b47d0ac46485