Code reference header does not require subsection

[siobhan]

Currently the code reference shows the subsection headings in the header for:

Code Reference: Hooks
Code Reference: Functions
Code Reference: Classes

The header should only read "Code Reference" throughout for two reasons:

• maintaining consistency with the rest of WordPress.org.
• getting rid of redundancy (the breadcrumb trail underneath the header tells you where you are so it's not also required in the header).

[Rarst]

Fixed in ​https://github.com/Rarst/wporg-developer/commit/825b23bd2a5cffe73a4603927c3986a1e289291e