core (constants): removed pyjamas workaround

src/core/constants.py

@@ -17,12 +17,9 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-try:
-    import __pyjamas__  # do not import xdg when building Libervia
-    BaseDirectory = None
-except ImportError:
+from xdg import BaseDirectory
+if BaseDirectory is not None:
     from os.path import expanduser, realpath
-    from xdg import BaseDirectory
 
 
 class Const(object):