Rip out context_hosts checks

The remote host is now encoded in the builder name so we don't need
to check it. We'll just do an inspect to confirm the builder exists.

lib/kamal/commands/builder/base.rb

@@ -1,4 +1,3 @@
-
 class Kamal::Commands::Builder::Base < Kamal::Commands::Base
   class BuilderError < StandardError; end
 
@@ -14,10 +13,29 @@ class Kamal::Commands::Builder::Base < Kamal::Commands::Base
     docker :image, :rm, "--force", config.absolute_image
   end
 
+  def push
+    docker :buildx, :build,
+      "--push",
+      *platform_options,
+      "--builder", builder_name,
+      *build_options,
+      build_context
+  end
+
   def pull
     docker :pull, config.absolute_image
   end
 
+  def info
+    combine \
+      docker(:context, :ls),
+      docker(:buildx, :ls)
+  end
+
+  def buildx_inspect
+    docker :buildx, :inspect, builder_name
+  end
+
   def build_options
     [ *build_tags, *build_cache, *build_labels, *build_args, *build_secrets, *build_dockerfile, *build_target, *build_ssh ]
   end
@@ -35,14 +53,6 @@ class Kamal::Commands::Builder::Base < Kamal::Commands::Base
       )
   end
 
-  def context_hosts
-    :true
-  end
-
-  def config_context_hosts
-    []
-  end
-
   def first_mirror
     docker(:info, "--format '{{index .RegistryConfig.Mirrors 0}}'")
   end