config/trees: stable-rc add 6.18.y and remove EOL branches

Remove EOL branches (5.4.y, 6.7.y, 6.9.y, 6.10.y, 6.11.y, 6.13.y, 6.14.y,
6.15.y, 6.16.y and 6.17.y). Add current stable branch (6.18.y)

Signed-off-by: Ben Copeland <ben.copeland@linaro.org>

Author: bhcopeland

config/trees/stable-rc.yaml

@@ -1,10 +1,6 @@
 build_configs:
-  stable-rc_5.4: &stable-rc
+  stable-rc_5.10: &stable-rc
     tree: stable-rc
-    branch: 'linux-5.4.y'
-
-  stable-rc_5.10:
-    <<: *stable-rc
     branch: 'linux-5.10.y'
 
   stable-rc_5.15:
@@ -19,30 +15,10 @@ build_configs:
     <<: *stable-rc
     branch: 'linux-6.6.y'
 
-  stable-rc_6.7:
-    <<: *stable-rc
-    branch: 'linux-6.7.y'
-
-  stable-rc_6.9:
-    <<: *stable-rc
-    branch: 'linux-6.9.y'
-
-  stable-rc_6.10:
-    <<: *stable-rc
-    branch: 'linux-6.10.y'
-
-  stable-rc_6.11:
-    <<: *stable-rc
-    branch: 'linux-6.11.y'
-
   stable-rc_6.12:
     <<: *stable-rc
     branch: 'linux-6.12.y'
 
-  stable-rc_6.13:
-    <<: *stable-rc
-    branch: 'linux-6.13.y'
-
-  stable-rc_6.14:
+  stable-rc_6.18:
     <<: *stable-rc
-    branch: 'linux-6.14.y'
+    branch: 'linux-6.18.y'