[API] Providers get with identifier

Providers fetch objects using a full identifier.  This ensures a consistent
interface.

Related to https://github.com/nasa/openmct/issues/1279

src/api/objects/ObjectAPI.js

@@ -150,10 +150,6 @@ define([
                 throw new Error('Provider does not support [' + method + '].');
             }
 
-            if (method === 'get') {
-                return provider.get(identifier.key);
-            }
-
             return provider[method].apply(provider, arguments);
         };
     });