Remove native implementation of proto_lang_toolchain rule

PiperOrigin-RevId: 446995789

Author: kotlaja

src/main/java/com/google/devtools/build/lib/rules/proto/ProtoLangToolchain.java

@@ -28,7 +28,11 @@
 import com.google.devtools.build.lib.packages.StarlarkProviderIdentifier;
 import com.google.devtools.build.lib.packages.Type;
 
-/** Implements {code proto_lang_toolchain}. */
+/**
+ * Implements {code proto_lang_toolchain}.
+ *
+ * <p>This rule is implemented in Starlark. This class remains only for doc-gen purposes.
+ */
 public class ProtoLangToolchainRule implements RuleDefinition {
   private static final Label DEFAULT_PROTO_COMPILER =
       Label.parseAbsoluteUnchecked(ProtoConstants.DEFAULT_PROTOC_LABEL);
@@ -126,7 +130,7 @@ public Metadata getMetadata() {
     return RuleDefinition.Metadata.builder()
         .name("proto_lang_toolchain")
         .ancestors(BaseRuleClasses.NativeActionCreatingRule.class)
-        .factoryClass(ProtoLangToolchain.class)
+        .factoryClass(BaseRuleClasses.EmptyRuleConfiguredTargetFactory.class)
         .build();
   }
 }