singleusergroup_tests: Move plugin dependency from deps to runtime_deps

The singleusergroup__plugin dependency is incorrectly declared as
compiled dependency, even though it is only runtime dependency. This
was flagged by unused_deps utility.

Change-Id: I89b8c94bc44673d7bdfd69c6ca35383f01d48ee6

BUILD

diff --git a/BUILD b/BUILD
index 640dbf2..065cc7c 100644
--- a/BUILD
+++ b/BUILD
@@ -16,7 +16,6 @@
     srcs = glob(["src/test/java/**/*Test.java"]),
     tags = ["replication"],
     visibility = ["//visibility:public"],
-    deps = PLUGIN_TEST_DEPS + PLUGIN_DEPS + [
-        ":singleusergroup__plugin",
-    ],
+    runtime_deps = [":singleusergroup__plugin"],
+    deps = PLUGIN_TEST_DEPS + PLUGIN_DEPS,
 )