Updated passthrough serializers to be consistent

refs: https://github.com/TryGhost/Toolbox/issues/245

- There are several serializers which are "passthroughs" that return the response from the query
  function as-is.
- The intention here is to make them all look consistent so they're easy to spot and understand what they do

core/server/api/canary/utils/serializers/output/oembed.js

@@ -1,8 +1,8 @@
 const debug = require('@tryghost/debug')('api:canary:utils:serializers:output:oembed');
 
 module.exports = {
-    all(res, apiConfig, frame) {
+    all(data, apiConfig, frame) {
         debug('all');
-        frame.response = res;
+        frame.response = data;
     }
 };

core/server/api/canary/utils/serializers/output/redirects.js

@@ -1,5 +1,5 @@
 module.exports = {
-    all(response, apiConfig, frame) {
-        frame.response = response;
+    all(data, apiConfig, frame) {
+        frame.response = data;
     }
 };

core/server/api/canary/utils/serializers/output/schedules.js

@@ -1,5 +1,5 @@
 module.exports = {
-    all(model, apiConfig, frame) {
-        frame.response = model;
+    all(data, apiConfig, frame) {
+        frame.response = data;
     }
 };

core/server/api/canary/utils/serializers/output/slack.js

@@ -1,9 +1,9 @@
 const debug = require('@tryghost/debug')('api:canary:utils:serializers:output:slack');
 
 module.exports = {
-    all(themes, apiConfig, frame) {
+    all(data, apiConfig, frame) {
         debug('all');
 
-        frame.response = themes;
+        frame.response = data;
     }
 };

core/server/api/canary/utils/serializers/output/themes.js

@@ -1,9 +1,9 @@
 const debug = require('@tryghost/debug')('api:canary:utils:serializers:output:themes');
 
 module.exports = {
-    all(themes, apiConfig, frame) {
+    all(data, apiConfig, frame) {
         debug('all');
 
-        frame.response = themes;
+        frame.response = data;
     }
 };