Remove success loading bar after creating a cluster

[mtfranchetto]

Description

Remove the misleading success flashbar after the create cluster request is completed. It's misleading because cluster creation is an asynchronous process that can fail.

How Has This Been Tested?

Created a cluster and no green flashbar is displayed

PR Quality Checklist

• [ ] I added tests to new or existing code
• [ ] I removed hardcoded strings and used react-i18next library (useTranslation hook and/or Trans component), see an example here
• [ ] I made sure no sensitive info gets logged at any time in the codebase (see here) (e.g. no user info or details, no stacktraces, etc.)
• [ ] I made sure that any GitHub issue solved by this PR is correctly linked
• [ ] I checked that infrastructure/update_infrastructure.sh runs without any error
• [x] I checked that npm run build builds without any error
• [x] I checked that clusters are listed correctly
• [x] I checked that a new cluster can be created (config is produced and dry run passes)
• [ ] I checked that login and logout work as expected

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