Fix misleading uninstall message for managed profiles

The message now depends on the state of mAllUsers flag in
UninstallAppProgress activity:
- This app is required for some users or profiles and was uninstalled for
  others (if mAllUsers==true)
- This app is needed for your work profile and can't be uninstalled
  (if mAllUsers==false)

Bug: 28240714
Change-Id: Ia060aebd112d3e4c5fcaee02a777140f085abf87