Remove unused files in the PlatformIO package

Ported from 3571db6290ca1330bf6bc13a39fc61dbec800df1

CHANGELOG.md

@@ -6,6 +6,7 @@ HEAD
 
 * Fix warning `function returns incomplete class type` on IAR (issue #2001)
 * Fix `volatile bool` serialized as `1` or `0` instead of `true` or `false` (issue #2029)
+* Remove unused files in the PlatformIO package
 
 v6.21.4 (2023-12-07)
 -------

library.json

@@ -12,11 +12,9 @@
     "name": "Benoit Blanchon",
     "url": "https://blog.benoitblanchon.fr"
   },
-  "exclude": [
-    ".devcontainer",
-    ".github",
-    "extras"
-  ],
+  "export": {
+    "include": ["src", "examples", "LICENSE.txt", "ArduinoJson.h"]
+  },
   "frameworks": "*",
   "platforms": "*",
   "build": {