fix: Update jQuery filter removal syntax for 3.x compatibility

[shlomomdahan]

Manually tested.

This recent upgrade to jQuery 3.x in #140 breaks the existing functionality in https://github.com/jenkinsci/build-pipeline-plugin/blob/master/src/main/resources/au/com/centrumsystems/hudson/plugin/buildpipeline/extension/BuildCardExtension/buildCardTemplate.jelly#L64

[Error] TypeError: content.get(0).style.removeAttr is not a function. (In 'content.get(0).style.removeAttr('filter')', 'content.get(0).style.removeAttr' is undefined)
	_finish (jquery.fancybox-1.3.4.js:580)
	(anonymous function) (jquery.min.js:2:61095)
	c (jquery.min.js:2:25310)
	fireWith (jquery.min.js:2:26055)
	u (jquery.min.js:2:57809)
	(anonymous function) (jquery.min.js:2:62806)
	dt (jquery.min.js:2:57126)

After change, works as expected.

Testing done

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[basil]

Sorry about that and thanks for noticing this.

[basil]

Thanks for the PR!