title: Delete old activity instance when starting a new activity
body: <p>I'm looking to delete/remove an old activity instance when a new instance (of same activity) is created, however I need to maintain all other activities in back-stack (therefore FLAG_ACTIVITY_CLEAR_TOP won't suffice). </p>
  
  <p>E.g. say I have activities A, B &amp; C.
  I start: A -> B -> C -> B.
  On the start of the second B activity I need to remove the existing B activity.
  Therefore I now have: A -> C -> B running...</p>
  
  <p>Any help appreciated.</p>