Change MR file header dropdown title and tooltip

What does this MR do?

• Remove dropdown section header: as there's only one section really, so it's redundant.
• Change tooltip to "Options": it's the label for the MR/issue header actions on smaller screens.

Screenshots

Before	After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides

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