Add channel to Nimbus again somehow

.experimenter.yaml

@@ -1,15 +1,4 @@
 ---
-engine-settings:
-  description: Contains a set of settings for controlling the web engine configurations.
-  hasExposure: true
-  exposureDescription: ""
-  variables:
-    tabs-prioritization-enabled:
-      type: boolean
-      description: "If true, enables tabs prioritization feature."
-    total-cookie-protection-enabled:
-      type: boolean
-      description: "If true, enables the total cookie protection in all browsing modes."
 homescreen:
   description: The homescreen that the user goes to when they press home or new tab.
   hasExposure: true
@@ -66,14 +55,6 @@ nimbus-validation:
     settings-title:
       type: string
       description: The title of displayed in the Settings screen and app menu.
-onboarding:
-  description: The onboarding features displayed on homescreen.
-  hasExposure: true
-  exposureDescription: ""
-  variables:
-    sections-enabled:
-      type: json
-      description: This property provides a lookup table of whether or not the given section should be enabled.
 search-term-groups:
   description: A feature allowing the grouping of URLs around the search term that it came from.
   hasExposure: true