GR-9136: revert import signal patch

Author: cosminbasca

graalpython/lib-python/3/pdb.py

@@ -76,8 +76,7 @@
 import code
 import glob
 import pprint
-# TODO: reenable me when signal is suported (GR-9136)
-# import signal
+import signal
 import inspect
 import traceback
 import linecache