fix: adjust widget remove button to fit contextual menu

[thevoiceofzeke]

https://jira.doit.wisc.edu/jira/browse/MUMUP-3297: "As a person navigating MyUW via keyboard, I would like the less-often-used controls associated with widgets on my home tucked away into a contextual menu, so that the primary navigation is simpler."

Companion PR: uportal-app-framework #786

In this PR:

• Make removal button a menu item
• Change icon to delete icon
• Add button text
• Delete unused CSS

Screenshot

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