[dependabot] Remove stale directories from config

ghstack-source-id: 570399bc77529bf9fb005149cfd20ba59405b2bc
Pull Request resolved: #31073

Author: poteto

.github/dependabot.yml

@@ -40,11 +40,6 @@ updates:
     schedule:
       interval: "weekly"
     open-pull-requests-limit: 0
-  - package-ecosystem: "npm"
-    directory: "/fixtures/fiber-triangle"
-    schedule:
-      interval: "weekly"
-    open-pull-requests-limit: 0
   - package-ecosystem: "npm"
     directory: "/fixtures/fizz"
     schedule:
@@ -60,11 +55,6 @@ updates:
     schedule:
       interval: "weekly"
     open-pull-requests-limit: 0
-  - package-ecosystem: "npm"
-    directory: "/fixtures/flight-browser"
-    schedule:
-      interval: "weekly"
-    open-pull-requests-limit: 0
   - package-ecosystem: "npm"
     directory: "/fixtures/flight-esm"
     schedule: