Fix leak in EliasFanoCodingTest

Summary: `EliasFanoCompressedList` requires explicit freeing.

Reviewed By: lbrandy, philippv, yfeldblum, luciang

Differential Revision: D4855200

fbshipit-source-id: ccee44b6371ae743ef15a72af9b691d5b56e37c2

folly/experimental/test/EliasFanoCodingTest.cpp

@@ -158,6 +158,8 @@ TEST_F(EliasFanoCodingTest, BugLargeGapInUpperBits) { // t16274876
     ASSERT_EQ(kLargeValue, reader.value());
     ASSERT_EQ(0, reader.previousValue());
   }
+
+  list.free();
 }
 
 namespace bm {