Check that permalinks are still the same after migration

[mscroggs]

In particular, the following pages should not have moved:

• https://fenicsproject.org/code-of-conduct/
• https://fenicsproject.org/community/
• https://fenicsproject.org/documentation/
• https://fenicsproject.org/download/
• https://fenicsproject.org/fenics-2021/
• https://fenicsproject.org/fenics17/
• https://fenicsproject.org/fenics18/
• https://fenicsproject.org/fenics19/
• https://fenicsproject.org/google-summer-of-code-2017/
• https://fenicsproject.org/google-summer-of-code-2018/
• https://fenicsproject.org/people-of-fenics/