Resolve warnings from deprecated proto targets. (#328)

Author: jmwachtel

proto/BUILD

@@ -1,5 +1,5 @@
 load("@rules_proto//proto:defs.bzl", "proto_library")
-load("@rules_java//java:defs.bzl", "java_proto_library")
+load("@protobuf//bazel:java_proto_library.bzl", "java_proto_library")
 
 proto_library(
     name = "build_proto",