Remove ServerSideCommand

ServerSideCommand now just aggregates CommandWithConnection and
CommandWithRemoteApi, so it's arguably clearer for commands to just implement
both of these.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=211670031

java/google/registry/tools/CreateRegistrarCommand.java

@@ -39,7 +39,7 @@ import javax.annotation.Nullable;
 /** Command to create a Registrar. */
 @Parameters(separators = " =", commandDescription = "Create new registrar account(s)")
 final class CreateRegistrarCommand extends CreateOrUpdateRegistrarCommand
-    implements ServerSideCommand {
+    implements CommandWithConnection, CommandWithRemoteApi {
 
   private static final ImmutableSet<RegistryToolEnvironment> ENVIRONMENTS_ALLOWING_GROUP_CREATION =
       ImmutableSet.of(PRODUCTION, SANDBOX, UNITTEST);