Remove source_under_test to comply with new BUCK version

Change-Id: I9b1811409d88b8a89eab4b93cf2f9df6c263b078

BUCK

diff --git a/BUCK b/BUCK
index c56d0af..b7fea48 100644
--- a/BUCK
+++ b/BUCK
@@ -37,7 +37,6 @@
   name = 'events-log_tests',
   srcs = glob(['src/test/java/**/*.java']),
   labels = ['events-log'],
-  source_under_test = [':events-log__plugin'],
   deps = TEST_DEPS,
 )