Files are not deleted from platforms folder on `tns run` command

[Fatme]

Environment
Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: 4.2.3
• Cross-platform modules: next
• Android Runtime: next
• iOS Runtime: next
• Plugin(s): no matter

Describe the bug
In case when the user deletes some files from app folder, the files are not deleted from platforms folder.

To Reproduce

1. tns create myApp
2. tns run android/ios
3. Delete some file from app folder

Expected behavior
The file should be deleted from platforms folder.

PR that fixes the issue: https://github.com/NativeScript/nativescript-cli/pull/3945/files