Drop GitLab GDK from Internal Developer Platform Known Instances

GDK is a local development environment a contributor runs on their own
machine, not the centralized, deployed self-service platform this
pattern describes. Per Sebastian Spier's review on #926.

Author: rrrutledge

patterns/1-initial/internal-developer-platform.md

@@ -123,7 +123,7 @@ An IDP provides a solution to the competing forces of consistency, flexibility,
 
 ## Known Instances
 
-* **GitLab** - GitLab containerized their GitLab Development Kit (GDK), cutting new-contributor environment setup from roughly two hours (frequently failing) to under five minutes. This directly reduced time-to-first-contribution for both open source and InnerSource-style contributors. See: [Break the contribution wall](https://www.youtube.com/watch?v=d3igPlTr4Ag) (InnerSource Commons, 2026, by Raimund Hook).
+(known instances to be added)
 
 ## Status