title: Prevent FirebaseCrash.logcat() from logging to logcat
body: <p>I'm using Timber in my app with the <code>DebugTree</code>. I want to log all messages to Firebase crash reporting.</p>
  
  <pre><code>Timber.plant(object :  Timber.DebugTree() {
      override fun log(priority: Int, tag: String?, message: String?, t: Throwable?) {
          FirebaseCrash.logcat(priority, tag, message)
      }
  })
  </code></pre>
  
  <p>But now all messages are duplicated in logcat which looks like this</p>
  
  <pre><code>11-07 17:08:07.823 V/GoogleApiClientPlugin: Connected to GooglePlayClient
  11-07 17:08:07.823 V/GoogleApiClientPlugin: Connected to GooglePlayClient
  11-07 17:08:07.824 V/NearbyForegroundService: connected to Google Api Client
  11-07 17:08:07.824 V/NearbyForegroundService: connected to Google Api Client
  </code></pre>
  
  <p>I don't want to guard the call with <code>if (BuildConfig.DEBUG) { ... }</code> because the log should be attached to crashes which happen in debug builds, too.</p>
  
  <p>Fabric has the same behavior but I'm able to set the logger to silent <code>.logger(new SilentLogger())</code> which prevents duplicated log messages. Is there an API for Firebase?</p>