Remove job trees from pipelines

This was mostly already done when we created 'ProjectConfig' and
'ProjectPipelineConfig' classes.  Clean up the remaining leftover
code and comments.

Story: 2000786
Task: 3310
Change-Id: I8a0bfb2cd148c174bc7e0b5121f8c39ed1d4645b
diff --git a/tests/unit/test_scheduler.py b/tests/unit/test_scheduler.py
index 45b2257..ecf8ca5 100755
--- a/tests/unit/test_scheduler.py
+++ b/tests/unit/test_scheduler.py
@@ -251,9 +251,12 @@
         C.addApproval('code-review', 2)
 
         self.fake_gerrit.addEvent(A.addApproval('approved', 1))
-        self.fake_gerrit.addEvent(B.addApproval('approved', 1))
-        self.fake_gerrit.addEvent(C.addApproval('approved', 1))
+        self.waitUntilSettled()
 
+        self.fake_gerrit.addEvent(B.addApproval('approved', 1))
+        self.waitUntilSettled()
+
+        self.fake_gerrit.addEvent(C.addApproval('approved', 1))
         self.waitUntilSettled()
 
         # There should be one merge job at the head of each queue running