Remove commented out git installation

Git is present by default

Dockerfile

@@ -1,8 +1,5 @@
 FROM python:3.6.3
 
-# Git is required for repo2docker to work
-#RUN apk add --no-cache git
-
 RUN mkdir /tmp/src
 ADD . /tmp/src
 RUN pip3 install --no-cache-dir /tmp/src