iOS compile error: no visible @interface for 'CDVCommandDelegateImpl' declares the selector 'execute:'
Building on what Nazar said, the only difference of significance when creating a new app and comparing an existing platforms/ios/Classes folder was removing the execute method from MainViewController.m.
This clears up the build error for me.
I've fixed the same problem with
cordova platform remove ioscordova platform add ios
Run cordova create with new cordova version to create new project then copy AppDelegate and MainViewController over files in your "old" project. After that the error is gone.