refactor: simplify toolchain registration

Author: alexeagle

examples/lang_toolchains/BUILD

@@ -6,24 +6,13 @@ proto_lang_toolchain(
     command_line = "--python_out=%s",
     progress_message = "Generating Python proto_library %{label}",
     runtime = "@pypi//protobuf",
+    toolchain_type = "@rules_python//python/proto:toolchain_type",
 )
 
 proto_lang_toolchain(
     name = "protoc_java_toolchain",
     command_line = "--java_out=%s",
     progress_message = "Generating Java proto_library %{label}",
     runtime = "@protobuf-java_3_25_3//jar",
-)
-
-# Adapters to the register_toolchains call, adding the toolchain_type to above
-toolchain(
-    name = "protoc_py_toolchain.registration",
-    toolchain = ":protoc_py_toolchain",
-    toolchain_type = "@rules_python//python/proto:toolchain_type",
-)
-
-toolchain(
-    name = "protoc_java_toolchain.registration",
-    toolchain = ":protoc_java_toolchain",
     toolchain_type = "@rules_java//java/proto:toolchain_type",
 )