Duplication of autodoc between the "coercion"/"categories" and "algebras"/"combinat" manuals

[mkoeppe]

For example these two are the same:

• https://doc.sagemath.org/html/en/reference/coercion/sage/categories/pushout.html
• https://doc.sagemath.org/html/en/reference/categories/sage/categories/pushout.html

Also these two:

• https://doc.sagemath.org/html/en/reference/algebras/sage/combinat/diagram_algebras.html
• https://doc.sagemath.org/html/en/reference/combinat/sage/combinat/diagram_algebras.html

In the index, these duplications can be spotted by looking for "[1]" https://doc.sagemath.org/html/en/reference/genindex-P.html