docs: remove Yarn upgrade/downgrade best practices

Author: MikeMcC399

docs/BestPractices.md

@@ -6,9 +6,6 @@
 
 - [Environment Variables](#environment-variables)
 - [Global npm dependencies](#global-npm-dependencies)
-- [Upgrading/downgrading Yarn](#upgradingdowngrading-yarn)
-  - [Local](#local)
-  - [Global](#global)
 - [Handling Kernel Signals](#handling-kernel-signals)
 - [Non-root User](#non-root-user)
 - [Memory](#memory)
@@ -38,54 +35,6 @@ ENV NPM_CONFIG_PREFIX=/home/node/.npm-global
 ENV PATH=$PATH:/home/node/.npm-global/bin # optionally if you want to run npm global bin without specifying path
 ```
 
-## Upgrading/downgrading Yarn
-
-### Local
-
-If you need to upgrade/downgrade `yarn` for a local install, you can do so by issuing the following commands in your `Dockerfile`:
-
-> Note that if you create some other directory which is not a descendant one from where you ran the command, you will end up using the global (dated) version. If you wish to upgrade `yarn` globally, follow the instructions in the next section.
-
-> When following the local install instructions, due to duplicated yarn the image will end up being bigger.
-
-```Dockerfile
-FROM node:6
-
-ENV YARN_VERSION=1.16.0
-
-RUN yarn policies set-version $YARN_VERSION
-```
-
-### Global
-
-```Dockerfile
-FROM node:6
-
-ENV YARN_VERSION=1.16.0
-
-RUN curl -fSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz" \
-    && tar -xzf yarn-v$YARN_VERSION.tar.gz -C /opt/ \
-    && ln -snf /opt/yarn-v$YARN_VERSION/bin/yarn /usr/local/bin/yarn \
-    && ln -snf /opt/yarn-v$YARN_VERSION/bin/yarnpkg /usr/local/bin/yarnpkg \
-    && rm yarn-v$YARN_VERSION.tar.gz
-```
-
-If you're using an Alpine-based image, `curl` won't be present, so you'll need to make sure it's installed while using it:
-
-```Dockerfile
-FROM node:6-alpine
-
-ENV YARN_VERSION=1.5.1
-
-RUN apk add --no-cache --virtual .build-deps-yarn curl \
-    && curl -fSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz" \
-    && tar -xzf yarn-v$YARN_VERSION.tar.gz -C /opt/ \
-    && ln -snf /opt/yarn-v$YARN_VERSION/bin/yarn /usr/local/bin/yarn \
-    && ln -snf /opt/yarn-v$YARN_VERSION/bin/yarnpkg /usr/local/bin/yarnpkg \
-    && rm yarn-v$YARN_VERSION.tar.gz \
-    && apk del .build-deps-yarn
-```
-
 ## Handling Kernel Signals
 
 Node.js was not designed to run as PID 1 which leads to unexpected behaviour when running inside of Docker. For example, a Node.js process running as PID 1 will not respond to `SIGINT` (`CTRL-C`) and similar signals. As of Docker 1.13, you can use the `--init` flag to wrap your Node.js process with a [lightweight init system](https://github.com/krallin/tini) that properly handles running as PID 1.