Remove deprecated button in project_selector/project_list_item.vue

What does this MR do?

Remove deprecated button and close #219895 (closed)

Screenshots

Resting before	Selected before	Focus before	Hover before

Resting after	Selected after	Focus after	Hover after

Instructions

• Using the migration script, or by manually editing the files:
  • Replace each instance of <gl-deprecated-button> with <gl-button>.
  • Convert each variant attribute to the new variant/category combination using the variant mapping guide.
• Take before/after screenshots of each button in the file, and upload them in the Merge Request description.
• Request review from a designer within your stage group. If you are outside of a stage group, ping a UX foundations member.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team