Replace use of depricated PRODUCT_RELEASE_NAME with SLIM_BUILD

PRODUCT_RELEASE_NAME has been removed from use by everything apart from squisher.
This should do exactly the same and allow us to clean up our device.mk files.
Currently we have both PRODUCT_RELEASE_NAME and PRODUCT_DEVICE defined exactly the same.

Change-Id: I90051d8b63c1f255f310a8f4b848f68254d4f5dd