In 40-make-app, also rm testbox/TES3MP.app

Otherwise, the resulting app includes a lot of unintended files:

1. After first run, `testbox/TES3MP.app/` exists
2. At beginning of second run, line 8 `rm -rf testbox/OpenMW.app` does
   nothing
3. At end of second run, line 64 `mv testbox/OpenMW.app
   testbox/TES3MP.app` results in `testbox/TES3MP.app/OpenMW.app/`

40-make-app.sh

@@ -5,7 +5,7 @@ set -ex
 readonly OSG_VERSION="3.6.5"
 
 mkdir -p testbox
-rm -rf testbox/OpenMW.app
+rm -rf testbox/OpenMW.app testbox/TES3MP.app
 cp -R out/src/TES3MP/build/OpenMW.app testbox/OpenMW.app
 mkdir -p testbox/OpenMW.app/Contents/Frameworks
 mkdir -p testbox/OpenMW.app/Contents/PlugIns