Remove changes to python version. (#1826)
This didn't work and breaks too many tools.
Undoes 89b700258aca7c8c254f5a077157d2c0565c6f25, turns out #1823 was a
bad idea.
diff --git a/buildkite/docker/centos7/Dockerfile b/buildkite/docker/centos7/Dockerfile
index 90ca178..f0fbf0c 100644
--- a/buildkite/docker/centos7/Dockerfile
+++ b/buildkite/docker/centos7/Dockerfile
@@ -155,7 +155,3 @@
rm -rf /usr/local/src/tar-1.34 && \
ln -s tar /usr/local/bin/gtar
-# Ensure python3.6 (installed earlier) is the default.
-# NOTE: This has to be after every `yum` command because the version of yum in Centos 7 is a python 2 app.
-RUN update-alternatives --install /usr/bin/python python /usr/bin/python3.6 60
-
