Fix flaky wiki create test

What does this MR do?

There's an svg on the page that allows you to create a wiki page. The svg takes a fraction of a second to load after which the "Create your first page" button shifts up a bit. This can cause webdriver to miss the hit so we wait for the svg to load before clicking the button.

Also update the elements used in the test to conform to our best practice.

And replace act with perform

Finally, remove the before block and login method, making the code slightly simpler.

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/quality/nightly/issues/24

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• [-] Documentation created/updated via this MR
• [-] Documentation reviewed by technical writer or follow-up review issue created
• [-] Tests added for this feature/bug
• [-] Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• [-] Security reports checked/validated by reviewer