title: Drop measurement that belong to a specific retention policy
body: <p>Recently, we migrated our data from measurement 'users' with retention policy autogen (default) to retention policy sixty_days (sixty_days.users).
  So we don't need anymore the data in autogen.users. </p>
  
  <p>How can we remove it without harming the data in sixty_days.users?</p>
  
  <p>This is a strange behavior because when we insert data to sixty_days.users - it's not applied on autogen.users, but when we try to delete / drop - it removes it from both of them.</p>
  
  <p>We tried to use DROP, and DELETE by time, but without success.</p>
  
  <p>We expect to remove only data in a measurement that belongs to a specific RT.</p>