mergify: simplify the script

Already assumed labels should not be checked again, lets keep it simple.

Author: 0xc0170

.mergify.yml

@@ -15,14 +15,16 @@
 # limitations under the License.
 
 # Mergify follow our workflow: https://os.mbed.com/docs/mbed-os/latest/contributing/workflow.html
+# Inital state is done by internal reviewer bot
+
+# Notes: conditions do not check if label is already there if we add or remote, this is to limit Github API access to
+# minimum. If a label is already there and we add it again, nothing bad happens (we gain 1 less access).
+# For instance for needs: work if CI failed, we just add a label as action.
 
 pull_request_rules:
+  # From review to needs: work - reviewers request
   - name: "label needs: work when changes were requested"
     conditions:
-      # Labels
-      - "label!=needs: work"
-      - "label!=needs: preceding PR"
-
       # Reviewers
       - "#changes-requested-reviews-by>0"
     actions:
@@ -32,12 +34,9 @@ pull_request_rules:
         remove: 
           - "needs: review"
 
+  # From review to needs: work - CI failure
   - name: "label needs: work when travis-ci failed"
     conditions:
-      # Labels
-      - "label!=needs: work"
-      - "label!=needs: preceding PR"
-
       # Travis failing
       - status-failure~=continuous-integration/travis-ci/pr
     actions:
@@ -47,6 +46,7 @@ pull_request_rules:
         remove: 
           - "needs: review"
 
+  # From review to needs: work - CI failure
   - name: "label needs: work when Jenkins CI failed - pr head"
     conditions:
       # Jenkins CI failing
@@ -55,7 +55,10 @@ pull_request_rules:
       label:
         add: 
           - "needs: work"
+        remove: 
+          - "needs: review"
 
+  # From review to needs: work - CI failure
   - name: "label needs: work when Jenkins CI failed - any of the pipeline"
     conditions:
       # Jenkins CI failing - any of the pipeline
@@ -64,6 +67,8 @@ pull_request_rules:
       label:
         add: 
           - "needs: work"
+        remove: 
+          - "needs: review"
 
   - name: "label needs: CI when at least one reviewers approval"
     conditions:
@@ -127,9 +132,6 @@ pull_request_rules:
     conditions:
       # Labels
       - label!=do not merge
-      - "label!=needs: work"
-      - "label!=needs: preceding PR"
-      - "label!=needs: review"
       - "label=needs: CI"
 
       # Reviewers