Use stable branches for gz-rendering8 and sdformat14 (#68)

Signed-off-by: Addisu Z. Taddese <addisu@openrobotics.org>

Author: azeey

plugins/config/repository.yaml

@@ -86,12 +86,6 @@ projects:
             type: stable
           - name: osrf
             type: nightly
-    - name: gz-rendering8
-      repositories:
-          - name: osrf
-            type: stable
-          - name: osrf
-            type: nightly
     - name: gz-sensors8
       repositories:
           - name: osrf
@@ -116,12 +110,6 @@ projects:
             type: stable
           - name: osrf
             type: nightly
-    - name: sdformat14
-      repositories:
-          - name: osrf
-            type: stable
-          - name: osrf
-            type: nightly
     # generic regexp
     - name: gazebo.*
       repositories: