Python: Make import python private in Concepts.qll

Just a mistake that we have never caught on to

Author: RasmusWL

python/ql/src/semmle/python/Concepts.qll

@@ -4,7 +4,7 @@
  * provide concrete subclasses.
  */
 
-import python
+private import python
 private import semmle.python.dataflow.new.DataFlow
 private import semmle.python.dataflow.new.RemoteFlowSources
 private import semmle.python.dataflow.new.TaintTracking