Re-enable vega test: chart should have some initial vega spec text

[tylersmalley]

In #20127 we disabled a test which was consecutively failing on master. We should investigate that failure and re-enable the test.

14:14:22          │ info  Saving page source to: /var/lib/jenkins/workspace/elastic+kibana+master+multijob-selenium/kibana/test/functional/failure_debug/html/visualize app visualize app vega chart should have some initial vega spec text.html
14:14:22        └- ✖ fail: "visualize app visualize app vega chart should have some initial vega spec text"
14:14:22        │        [GET http://localhost:9515/session/2555b60b9c10e0cc2cf85bd82cbed6f1/element/0.5071927360771173-18/text] stale element reference: element is not attached to the page document
14:14:22        │         (Session info: chrome=65.0.3325.162)
14:14:22        │         (Driver info: chromedriver=2.36.540471 (9c759b81a907e70363c6312294d30b6ccccc2752),platform=Linux 4.4.0-1050-aws x86_64)
14:14:22        │         at Server._get (test/functional/services/remote/verbose_remote_logging.js:22:21)
14:14:22        │         at runRequest (node_modules/leadfoot/Session.js:92:40)
14:14:22        │         at getFinalValue (node_modules/dojo/Promise.js:258:35)
14:14:22        │         at node_modules/dojo/Promise.js:272:24
14:14:22        │         at node_modules/dojo/Promise.js:156:41
14:14:22        │         at runCallbacks (node_modules/dojo/Promise.js:19:22)
14:14:22        │         at node_modules/dojo/Promise.js:103:21
14:14:22        │         at run (node_modules/dojo/Promise.js:51:33)
14:14:22        │         at node_modules/dojo/nextTick.js:35:17
14:14:22        │         at _combinedTickCallback (internal/process/next_tick.js:131:7)
14:14:22        │         at process._tickCallback (internal/process/next_tick.js:180:9)

[alexwizp]

This issue was in scope of #72238. Thank you @flash1293