remove redundant symbolic link creation

Dockerfile tries to create an already existing symbolic link from
python2.7 to python (such link is created by default when installing
python package).

This creates some noise in the logs.

Remove useless instruction

Dockerfile

@@ -30,7 +30,7 @@ RUN apt-get update && apt-get install -y  \
     apt-get autoremove -y && \
     pip install ws4py==0.3.2 && \
     pip install tornado && \    
-    ln -s /usr/bin/python2.7 /usr/bin/python ; ln -s -f bash /bin/sh
+    ln -s -f bash /bin/sh
 
 WORKDIR /opt