Move native remote to just remote

It's just a remote builder, that will build whichever platform is asked
for, so let's remove the "native" part.

We'll also remove the service name from the builder name, so multiple
services can share the same builder.

lib/kamal/commands/builder.rb

@@ -19,7 +19,7 @@ class Kamal::Commands::Builder < Kamal::Commands::Base
     when config.builder.local? && config.builder.remote?
       multiarch_remote
     when config.builder.remote?
-      native_remote
+      remote
     else
       local
     end
@@ -29,8 +29,8 @@ class Kamal::Commands::Builder < Kamal::Commands::Base
     @native ||= Kamal::Commands::Builder::Native.new(config)
   end
 
-  def native_remote
-    @native ||= Kamal::Commands::Builder::Native::Remote.new(config)
+  def remote
+    @remote ||= Kamal::Commands::Builder::Remote.new(config)
   end
 
   def local