Update tree-building exercise file configuration

Author: Jegors Cemisovs

exercises/practice/tree-building/.meta/config.json

@@ -22,9 +22,7 @@
       ".meta/src/reference/java/BuildTree.java"
     ],
     "editor": [
-      "src/main/java/InvalidRecordsException.java",
-      "src/main/java/Record.java",
-      "src/main/java/TreeNode.java"
+      "src/main/java/InvalidRecordsException.java"
     ],
     "invalidator": [
       "build.gradle"