Do not commit examples spec files

[bahmutov]

When we bundle cypress-example-kitchensink example specs, we copy them and commit to the repo. This leads to the duplication and makes updating cypress-example-kitchensink version hard (have to remember to run npm run build!)

Instead we should just "build" the example when building the test runner binary and not commit these files

[brian-mann]

I believe we just need to add packages/example/cypress to .gitignore and delete the existing files.

The binary building process already runs the appropriate npm run build steps to ensure that the latest files are copied over from the kitchensink.

[cypress-bot]

The code for this is done in cypress-io/cypress#4862, but has yet to be released.
We'll update this issue and reference the changelog when it's released.

[cypress-bot]

Released in 3.4.1.