Remove usages of dropdown-menu-close from specs and QA tests

Summary

During the refactoring of the times FA icon (!40585 (merged)), it was noticed that we are using the dropdown-menu-close/dropdown-menu-close-icon classes within a variety of specs and QA tests.

This means that although we aren't using the underlying jQuery functionality, we can't remove these unused classes.

We should update the specs and QA tests to use better identifiers and remove these classes where appropriately covered by other mechanisms (e.g. Vue events).

Improvements

Removing these will make our older code less coupled to our older jQuery implementations and in turn, reduce our reliance on unstable classes in our specs and QA tests.

This will make future rewrites easier to manage and reduce the time it takes to complete them.

Risks

The two main risks are:

1. Failing tests as a result of this change, which should be covered by running each test locally and within our pipelines
2. Failing functionality/styles caused by this removal. We should test that the associated dropdowns still work as expected after this change.