Remove source_under_test to comply with latest buck version

Change-Id: I72b1479517aa41406ce466a8eb63ff653abcc9a8

BUCK

diff --git a/BUCK b/BUCK
index 289b610..4ee53bf 100644
--- a/BUCK
+++ b/BUCK
@@ -31,5 +31,4 @@
     '//lib/log:log4j',
     '//lib/log:impl_log4j',
   ],
-  source_under_test = [':quota__plugin'],
 )