Bazel: Replace deprecated dependency mode LOOSE with PRUNE_LEGACY

This fixes this warning in closure_js_binary rule:

  dependency_mode=LOOSE is deprecated and will be removed soon;
  prefer to use its equivalent PRUNE_LEGACY

that was added in this PR: [1].

[1] https://github.com/bazelbuild/rules_closure/pull/444

Change-Id: I648f581a8f585402543b97ce7a7ef056ca298c3e

polygerrit-ui/app/rules.bzl

@@ -20,6 +20,7 @@ def polygerrit_bundle(name, srcs, outs, app):
         ],
         language = "ECMASCRIPT5",
         deps = [name + "_closure_lib"],
+        dependency_mode = "PRUNE_LEGACY",
     )
 
     # TODO(davido): Remove JSC_REFERENCE_BEFORE_DECLARE when this is fixed upstream:

tools/bzl/js.bzl

@@ -484,6 +484,7 @@ def polygerrit_plugin(name, app, srcs = [], deps = [], assets = None, plugin_nam
         deps = [
             name + "_closure_lib",
         ],
+        dependency_mode = "PRUNE_LEGACY",
     )
 
     if html_plugin: