Remove DefaultSelectionToolbarRenderService

This implementation is obsolete and untested since the system ui
implementation is used in development and testing. We remove it to end
risk of incompatible divergence between the implementations.

Fixes: 435444047
Flag: android.permission.flags.system_selection_toolbar_enabled
Test: Validate toolbar works after disabling
          use_system_selection_toolbar_in_sysui flag
Change-Id: I17b253309943f2a7abd90966de982dfad4124dd1