Remove unused code (#1570)

This code is not being used and looks to be a duplicate of
ARG_PODCAST_URI in the companion object. This could lead to unexpected
issues in the future.

Noticed while reading thru the code and just wanted to contribute back 😁

Author: riggaroo

Jetcaster/mobile/src/main/java/com/example/jetcaster/ui/JetcasterAppState.kt

@@ -43,8 +43,6 @@ sealed class Screen(val route: String) {
     }
 
     object PodcastDetails : Screen("podcast/{$ARG_PODCAST_URI}") {
-
-        val PODCAST_URI = "podcastUri"
         fun createRoute(podcastUri: String) = "podcast/$podcastUri"
     }