JENKINS-71246 Remove animations on login page causing high CPU usage in some cases

[timja]

See JENKINS-71246

Testing done

I was not able to reproduce the issue so I'll ask someone to test the build who can reproduce it.
I've ran the change and it's not animating any more:

Proposed changelog entries

• JENKINS-71246 Remove animations on login page causing high CPU usage in some cases

Proposed upgrade guidelines

N/A

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@mention

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[daniel-beck]

While it wasn't as bad as described by some for me, it's a very significant improvement.

weekly.ci vs PR build

Firefox

Before

After

Chrome

Before

After

[mawinter69]

I can confirm that on chrome and firefox GPU usage drops to near zero on windows.

[timja]

good enough for now then

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/label ready-for-merge

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This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.

Thanks!