Bazel: Switch to using bazlets

We prefer to consume maven_jar custom rule from bazlets repository, for
the same reasons as in Gerrit project:

* caching atifacts across different clones and projects
* exposing source classifiers and neverlink artifact

Change-Id: Ia560a68136186025926649f6985608fcf326082f

gitiles-servlet/BUILD

diff --git a/gitiles-servlet/BUILD b/gitiles-servlet/BUILD
index ff33933..e19f329 100644
--- a/gitiles-servlet/BUILD
+++ b/gitiles-servlet/BUILD
@@ -51,7 +51,7 @@
     ],
 )
 
-load("//gitiles-servlet:junit.bzl", "junit_tests")
+load("@com_googlesource_gerrit_bazlets//tools:junit.bzl", "junit_tests")
 
 junit_tests(
     name = "ServletTests",