Lexicons, remove invalid concrete schema

lexicons/my/spoor/content/external.json

@@ -14,7 +14,7 @@
             "minLength": 1,
             "items": {
               "type": "ref",
-              "ref": "my.spoor.content.defs#title"
+              "ref": "my.spoor.content.title"
             }
           },
           "source": {

lexicons/my/spoor/content/media.json

@@ -14,7 +14,7 @@
             "minLength": 1,
             "items": {
               "type": "ref",
-              "ref": "my.spoor.content.defs#title"
+              "ref": "my.spoor.content.title"
             }
           },
           "durationData": {

lexicons/my/spoor/content/title.json

@@ -1,17 +1,15 @@
 {
   "lexicon": 1,
-  "id": "my.spoor.content.defs",
+  "id": "my.spoor.content.title",
   "defs": {
-    "title": {
+    "main": {
       "type": "object",
       "properties": {
         "translationType": { 
           "type": "string",
           "format": "nsid",
           "knownValues": [
-            "my.spoor.content.defs#titleHomophonic",
-            "my.spoor.content.defs#titleNative",
-            "my.spoor.content.defs#titleTranslation"
+            "#titleHomophonic", "#titleNative", "#titleTranslation"
           ]
         },
         "lang": {

lexicons/my/spoor/log/activity.json

@@ -15,7 +15,7 @@
           "progress": {
             "type": "union",
             "refs": [
-              "my.spoor.log.activity#indexProgress"
+              "#progressIndex"
             ]
           },
           "performedAt": {
@@ -31,9 +31,13 @@
         }
       }
     },
-    "indexProgress": {
-      "type": "integer",
-      "description": "The index of the content consumed. Content must be indexable"
+    "progressIndex": {
+      "type": "object",
+      "description": "The index of the content consumed. Content must be indexable",
+      "required": [ "index" ],
+      "properties": {
+        "index": { "type": "integer" }
+      }
     }
   }
 }