Remove Py2 code from common_utils (#691)

torchaudio/common_utils.py

-import sys
-
-PY3 = sys.version_info > (3, 0)
-PY34 = sys.version_info >= (3, 4)
+import importlib.util
 
 
 def _check_module_exists(name: str) -> bool:
@@ -11,28 +8,10 @@ def _check_module_exists(name: str) -> bool:
     our tests, e.g., setting multiprocessing start method when imported
     (see librosa/#747, torchvision/#544).
     """
-    if not PY3:  # Python 2
-        import imp
-        try:
-            imp.find_module(name)
-            return True
-        except ImportError:
-            return False
-    elif not PY34:  # Python [3, 3.4)
-        import importlib
-        loader = importlib.find_loader(name)
-        return loader is not None
-    else:  # Python >= 3.4
-        import importlib
-        import importlib.util
-        spec = importlib.util.find_spec(name)
-        return spec is not None
+    spec = importlib.util.find_spec(name)
+    return spec is not None
 
 IMPORT_NUMPY = _check_module_exists('numpy')
 IMPORT_KALDI_IO = _check_module_exists('kaldi_io')
 IMPORT_SCIPY = _check_module_exists('scipy')
-
-# On Py2, importing librosa 0.6.1 triggers a TypeError (if using newest joblib)
-# see librosa/librosa#729.
-# TODO: allow Py2 when librosa 0.6.2 releases
-IMPORT_LIBROSA = _check_module_exists('librosa') and PY3
+IMPORT_LIBROSA = _check_module_exists('librosa')