Remove rx send remote config and group send using rx always.

app/src/main/java/org/thoughtcrime/securesms/dependencies/ApplicationDependencyProvider.java

@@ -144,8 +144,7 @@ public class ApplicationDependencyProvider implements AppDependencies.Provider {
                                             provideGroupsV2Operations(signalServiceConfiguration).getProfileOperations(),
                                             SignalExecutors.newCachedBoundedExecutor("signal-messages", ThreadUtil.PRIORITY_IMPORTANT_BACKGROUND_THREAD, 1, 16, 30),
                                             ByteUnit.KILOBYTES.toBytes(256),
-                                            RemoteConfig.okHttpAutomaticRetry(),
-                                            RemoteConfig.useRxMessageSending());
+                                            RemoteConfig.okHttpAutomaticRetry());
   }
 
   @Override

app/src/main/java/org/thoughtcrime/securesms/util/RemoteConfig.kt

@@ -968,15 +968,6 @@ object RemoteConfig {
     hotSwappable = true
   )
 
-  /** Use Rx threading model to do sends.  */
-  @JvmStatic
-  @get:JvmName("useRxMessageSending")
-  val useRxMessageSending: Boolean by remoteBoolean(
-    key = "android.rxMessageSend.2",
-    defaultValue = false,
-    hotSwappable = true
-  )
-
   /** The lifespan of a linked device (i.e. the time it can be inactive for before it expires), in milliseconds.  */
   @JvmStatic
   val linkedDeviceLifespan: Long by remoteValue(