Remove Python 2 support

Python 2 is long dead and devlib does not support it anymore, so cleanup
old Python 2-only code.

wa/framework/version.py

@@ -57,7 +57,4 @@ def get_commit():
     p.wait()
     if p.returncode:
         return None
-    if sys.version_info[0] == 3 and isinstance(std, bytes):
-        return std[:8].decode(sys.stdout.encoding or 'utf-8')
-    else:
-        return std[:8]
+    return std[:8].decode(sys.stdout.encoding or 'utf-8')