[test] remove custom implementation of FakeRequest.header_accept_language() (closes #3375021)
``Accept-Language`` should be overridable just as any other request header.
Default value is "nothing" since the application should be able the empty
header case.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html