Various python3 related changes

- Use relative import for grgsm's modules
- Convert map to list
- Remove the hier_block.py workaround as as gnuradio 3.7 is no longer
  supported in this branch

Change-Id: I5ca8fd340823996e8c444aaf18ddacd85c92ab1c
diff --git a/apps/grgsm_decode b/apps/grgsm_decode
index 4bd1d95..034014e 100755
--- a/apps/grgsm_decode
+++ b/apps/grgsm_decode
@@ -336,7 +336,7 @@
         parser, 'TCH Options', 'Options for setting Traffic channel decoding parameters.',
     )
     tch_options.add_option("-d", "--speech-codec", dest="speech_codec", default='FR',
-                           type='choice', choices=tch_codecs.keys(),
+                           type='choice', choices=list(tch_codecs.keys()),
                            help="TCH-F speech codec [default=%default]. "
                                 "Valid options are " + ", ".join(tch_codecs.keys()))
     tch_options.add_option("-o", "--output-tch", dest="speech_output_file", default="/tmp/speech.au.gsm",