Delete stripped debug information when building for Android
We currently don't do anything with those, but they can find their way into the APK package and unnecessarily bloat that.
This isn't a problem for normal libraries in lib/, but plugins located elsewhere and moved/renamed by androiddeployqt leave their .debug files behind and then can end up in the APK.
This reduces the APK size for basic Kirigami apps like Kongress by ~15Mb.