Fix buck build, remove java_test.source_under_test

This parameter is not required any more after latest buck upgrade.

Change-Id: I1432850c105c148c20a8210b66673d84ee0aa92b
diff --git a/BUCK b/BUCK
index e48994b..749b4c8 100644
--- a/BUCK
+++ b/BUCK
@@ -34,7 +34,6 @@
   name = 'events-log_tests',
   srcs = glob(['src/test/java/**/*.java']),
   labels = ['events-log'],
-  source_under_test = [':events-log__plugin'],
   deps = TEST_DEPS,
 )