fix: gc.collect() of dependent elements

cycle-reference may exist between an element and a traceback
stored in SardanaValue or SardanaAttribute as a consequence of
getting sys.exc_info(). Keeping a list of dependent elements in the
scope of delete_element() makes it impossible to gc.collect() to
collect the cycled objects. Use has_dependent_elements() in order
to determine if there are dependent elements and then call the
gc.collect(). Also, do not call it conditionally only for the pseudo counters
but for any element type - the cycle may be created for between any
alement and a traceback.

src/sardana/pool/pool.py

@@ -560,15 +560,12 @@ def delete_element(self, name):
                 elem = self.get_element(full_name=name)
             except:
                 raise Exception("There is no element with name '%s'" % name)
-
-        # TODO: most probably due to some cycle-reference the psuedo counter
-        #  objects are not being deleted when undefining them, as a workaround
-        #  try to delete them with gc.collect()
-        dependent_elements = elem.get_dependent_elements()
-        for dependent_element in dependent_elements:
-            if dependent_element.get_type() == ElementType.PseudoCounter:
-                gc.collect()
-                break
+
+        # cycle-reference may exist between the element and a traceback
+        # stored in SardanaValue or SardanaAttribute as a consequence of
+        # getting sys.exc_info() - try to delete them with gc.collect()
+        if elem.has_dependent_elements():
+            gc.collect()
 
         dependent_elements = elem.get_dependent_elements()
         if len(dependent_elements) > 0: