Remove .issue-box from static (classic) Issuable list

What does this MR do?

Removes %div.issue-box from static (classic) Issuable lists (i.e. Dashboard Issues, Project Issues, Group Issues).

Quoting #284602 (closed):

.issue-box can be removed since .issue-box is just for display: flex, duplicating of issuable-info-container, which has flex: 1; display: flex; /* and more ... */.

Screenshots (strongly suggested)

There is no regression on show and on edit:

on issue list (show)

on issue list (bulk edit)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Part of #284602 (closed)