Revert "Fix for UnicodeEncodeError in search"

This reverts commit 4a3240bf1a.

VM names never contain any unicode characters, so this fix only
propagates the possibility of an encoding error to further down
the line, rather than removing it.

A proper fix would involve filtering the input to the search box
as we do with creating & renaming VMs.

qubesmanager/main.py

@@ -719,7 +719,7 @@ class VmManagerWindow(Ui_VmManagerWindow, QMainWindow):
 
     @pyqtSlot(str)
     def do_search(self, search):
-        self.search = unicode(search)
+        self.search = str(search)
         self.showhide_vms()
         self.set_table_geom_size()