ci: Remove dead config in .travis.yml

[rhcarvalho]

There is no "Saucelabs" stage, and otherwise the "stages" entry just
serve to customize the order of the stages, which does not need to be
customized.

[getsentry-bot]

Fails

🚫

TSLint failed: @sentry/integrations ERROR: /home/travis/build/getsentry/sentry-javascript/packages/integrations/src/vue.ts[8, 24]: Type assertion on object literals is forbidden, use a type annotation instead. ERROR: /home/travis/build/getsentry/sentry-javascript/packages/integrations/src/vue.ts[239, 37]: Unsafe use of expression of type 'any'. ERROR: /home/travis/build/getsentry/sentry-javascript/packages/integrations/src/vue.ts[310, 11]: Unsafe use of expression of type 'any'.

	Warnings
⚠️	Please add a changelog entry for your changes.

	Messages
📖	@sentry/browser bundle gzip'ed minified size: (ES5: 17.1279 kB) (ES6: 16.1582 kB)

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