Alter memory management strategy post Tangram-es 0.7 work

[msmollin]

Description

Right now we currently do a bunch of juggling work around the fact that older versions of Tangram-es were following an older iOS memory management recommendation that would remove its view from the view hierarchy upon memory warnings.

As of the 0.6 series this is no longer the case and Tangram-es follows the modern iOS recommendations. Thus, we can remove most of our code that manages that process although we should make sure we coordinate these changes with the ES team.

cc @karimnaaji / @matteblair

[matteblair]

It should be much more straightforward to manage memory pressure with the newer approach. No special handling is needed for tangram, it will respond to memory warnings internally as best as it can.