Don't add a Run Script step to application targets

Recent versions of the Instabug CocoaPod include a `prepare_command` that adds a Run Script build step to each application target. The build step seems to upload a dSYM to Instabug. In my case, this is problematic because:

* I don't use Instabug's crash logging, so there's no benefit to uploading the dSYM.
* Uploading a dSYM is slow enough to have a noticeable effect on my build time.
* The build step is added to each application target, two of which are dependencies of my main target. So the slowdown is multiplied by three.
* If I `rm -r Pods; pod install`, then a duplicate build step appears in each target. So the slowdown is multiplied again by however many build steps have accumulated in this way.

There's no obvious way to prevent the `prepare_command` from running, so I had to remove it.