Fixes incorrect delete on app update

This change fixes an incorrect refactor of delete. During the refactor,
deletion of all nonsystem apps for an unspecified user changed from not
uninstalling to uninstalling. This change ensures that that only happens
when a user is specified.

Change-Id: I00f709a3aca09da0357454397da60ea398e28627
Fixes: 121201046
Fixes: 121237029
Test: atest InstantAppUserTest#testReplaceExisting