Migrate uses of config_windowIsRound to Configuration.isScreenRound

Move existing code that previously relied on config_windowIsRound to
use the new Configuration.isScreenRound() method. Also move the system
property override for emulators over to the initial setup of a Display
so that the configuration property is consistent with existing
expectations.

Remove config_windowIsRound from symbols.xml. The symbol now only
exists as a default value redirect for overlays already configured to
supply this value.

Change-Id: I24e6564030a6051c3ac7262868983b43e13eee65