Delete yarn instructions and lock files (#869)

* Delete yarn.lock files

* Delete yarn instructions

There is no reason not to use `npm` which comes bundled with Node.
If anybody wants to use `yarn`, the commands are the same
as those for `npm`, we don't need to clutter the `README`s with them.

CONTRIBUTING.md

@@ -35,16 +35,10 @@ For instructions regarding development environment setup, please visit [the docu
 ### How to run the tests
 
 1. You must install dependencies at the root of the `nodejs-docs-samples`
-directory. You can do so with `yarn` or `npm`:
+directory.
 
         npm install
 
-    or
-
-        yarn install
-
-    **Note:** Use `npm` *or* `yarn` exclusively, don't mix them.
-
 1. In a terminal, start Redis:
 
         redis-server
@@ -57,61 +51,33 @@ directory. You can do so with `yarn` or `npm`:
 
         npm test
 
-    or
-
-        yarn test
-
     With code coverage:
 
         npm run cover
 
-    or
-
-        yarn run cover
-
 1. Then run the system tests from the root of the project:
 
         npm run system-test
 
-    or
-
-        yarn run system-test
-
     With code coverage:
 
         npm run system-cover
 
-    or
-
-        yarn run system-cover
-
 1. Or run all the tests at once:
 
         npm run all-test
 
-    or
-
-        yarn run all-test
-
     With code coverage:
 
         npm run all-cover
 
-    or
-
-        yarn run all-cover
-
 ### Run the tests for a single sample
 
 1. You must install dependencies at the root of the `nodejs-docs-samples`
-directory. You can do so with `yarn` or `npm`:
+directory.
 
         npm install
 
-    or
-
-        yarn install
-
 1. Change directory to one of the sample folders, e.g. `bigquery`:
 
         cd bigquery/
@@ -121,22 +87,12 @@ directory. You can do so with `yarn` or `npm`:
         npm test
 
     or
-
-        yarn test
-
-    or
-
+
         npm run system-test
 
-    or
-
-        yarn run system-test
 
 ## Style
 
-Samples in this repository follow the [JavaScript Semi-Standard
-Style](https://github.com/Flet/semistandard).
-
 You can run `npm run lint` to match our JavaScript coding standards.
 
 ## Sample template

README.md

@@ -150,12 +150,6 @@ on Google Cloud Platform.
 
         npm install
 
-    or
-
-        yarn install
-
-    **Note:** Use `npm` *or* `yarn` exclusively, don't mix them.
-
 1. Run the sample:
 
         node sample_file.js [args]...

appengine/README.md

@@ -36,22 +36,15 @@ The App Engine Node.js samples typically that you do the following:
 
         cd appengine/sample-folder/
 
-1.  Install depedencies using `npm` or `yarn`:
+1.  Install depedencies:
 
         npm install
 
-    or
-
-        yarn install
-
-1.  Run the sample with `npm` or `yarn` (See the sample's `README.md` file for
+1.  Run the sample with `npm` (See the sample's `README.md` file for
     any additional setup):
 
         npm start
 
-    or
-
-        yarn start
 
 1.  Visit the application at [http://localhost:8080][].
 
@@ -93,9 +86,6 @@ Generally speaking, to deploy a sample application:
 
     to deploy the app to its compatible environment.
 
-    Note: If there is a `yarn.lock` file then `yarn install` will be used during
-    deployment. Delete the `yarn.lock` file to fall back to `npm install`.
-
 1.  View your deployed application at `https://YOUR_PROJECT_ID.appspot.com`.
 
 ## Official samples

appengine/analytics/README.md

@@ -22,24 +22,12 @@ Before you can run or deploy the sample, you need to do the following:
 1.  Add your tracking ID to `app.yaml`.
 1.  Install dependencies:
 
-    With `npm`:
-
         npm install
 
-    or with `yarn`:
-
-        yarn install
-
 ## Running locally
 
-With `npm`:
-
     GA_TRACKING_ID=YOUR_TRACKING_ID npm start
 
-or with `yarn`:
-
-    GA_TRACKING_ID=YOUR_TRACKING_ID yarn start
-
 ## Deploying to App Engine standard Environment
 
 ```

appengine/datastore/README.md

@@ -20,24 +20,12 @@ Before you can run or deploy the sample, you need to do the following:
     running and deploying.
 1.  Install dependencies:
 
-    With `npm`:
-
         npm install
 
-    or with `yarn`:
-
-        yarn install
-
 ## Running locally
 
-With `npm`:
-
     npm start
 
-or with `yarn`:
-
-    yarn start
-
 ## Deploying to App Engine standard environment
 
 	gcloud app deploy app.standard.yaml