schema: use pid, zone, stepwise schemas

These schemas were defined, but not referenced anywhere.  Use them, and
remove the duplicated properties from the legacy aggregate schema.

Change-Id: I75ba8099059127cfa5c2d6492908333ca5c3bf67
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/schemas/Pid.Zone.json b/schemas/Pid.Zone.json
index 86ff1e1..4e4e41a 100644
--- a/schemas/Pid.Zone.json
+++ b/schemas/Pid.Zone.json
@@ -1,24 +1,28 @@
 {
-    "$schema": "http://json-schema.org/schema#",
-    "type": "object",
-    "properties": {
-        "FailSafePercent": {
-            "type": "number"
-        },
-        "MinThermalOutput": {
-            "type": "number"
-        },
-        "Name": {
-            "type": "string"
-        },
-        "Type": {
-            "type": "string"
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "definitions": {
+        "PidZone": {
+            "type": "object",
+            "properties": {
+                "FailSafePercent": {
+                    "type": "number"
+                },
+                "MinThermalOutput": {
+                    "type": "number"
+                },
+                "Name": {
+                    "type": "string"
+                },
+                "Type": {
+                    "type": "string"
+                }
+            },
+            "required": [
+                "FailSafePercent",
+                "MinThermalOutput",
+                "Name",
+                "Type"
+            ]
         }
-    },
-    "required": [
-        "FailSafePercent",
-        "MinThermalOutput",
-        "Name",
-        "Type"
-    ]
+    }
 }