docs: Remove ADR toctree

Leftover from Sphinx/RTD, doesn't work with MkDocs.

docs/architectural-decisions.md

@@ -5,8 +5,5 @@ title: Architectural Decision Records
 We record major architectural decisions for Kitsune/SUMO in Architecture
 Decision Records (ADR), as [described by Michael
 Nygard](http://thinkrelevance.com/blog/2011/11/15/documenting-architecture-decisions).
-Below is the list of our current ADRs.
 
-::: {.toctree maxdepth="1" glob=""}
-architecture/decisions/\*
-:::
+Our current ADRs are listed in the navigation.