Bazel: Load java_proto_library from protobuf

The checks plugin still loads java_proto_library from rules_java, which
is deprecated and causes Bazel warnings during the build.

Switch the load statement to:
@protobuf//bazel:java_proto_library.bzl

This matches current Gerrit usage and removes the deprecation warnings
for cache_java_proto.

Change-Id: Ib9f4a8fb05b2585eb99044f0064ff158c27c3a18

proto/BUILD

diff --git a/proto/BUILD b/proto/BUILD
index 168ca6f..82c8885 100644
--- a/proto/BUILD
+++ b/proto/BUILD
@@ -1,7 +1,5 @@
+load("@protobuf//bazel:java_proto_library.bzl", "java_proto_library")
 load("@rules_proto//proto:defs.bzl", "proto_library")
-load("@rules_java//java:defs.bzl", "java_proto_library")
-
-package(default_visibility = ["//plugins/checks:visibility"])
 
 proto_library(
     name = "cache_proto",