Remove yarn >=3 version requirement (#328)

This removes the requirement for yarn version 3 or higher, which was
breaking user setups when they use this SDK with older yarn versions.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <[email protected]>

Author: jasonpraful

package.json

@@ -180,8 +180,7 @@
   },
   "packageManager": "[email protected]",
   "engines": {
-    "node": ">=18",
-    "yarn": ">=3"
+    "node": ">=18"
   },
   "codegenConfig": {
     "name": "IntercomReactNativeSpec",