Remove unused RxJavaCallAdapterFactory for app updater

app/src/main/java/eu/kanade/tachiyomi/data/updater/github/GithubService.kt

@@ -2,7 +2,6 @@ package eu.kanade.tachiyomi.data.updater.github
 
 import eu.kanade.tachiyomi.network.NetworkHelper
 import retrofit2.Retrofit
-import retrofit2.adapter.rxjava.RxJavaCallAdapterFactory
 import retrofit2.converter.gson.GsonConverterFactory
 import retrofit2.http.GET
 import uy.kohesive.injekt.Injekt
@@ -18,7 +17,6 @@ interface GithubService {
             val restAdapter = Retrofit.Builder()
                     .baseUrl("https://api.github.com")
                     .addConverterFactory(GsonConverterFactory.create())
-                    .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
                     .client(Injekt.get<NetworkHelper>().client)
                     .build()