Remove assert(s.ok()) from ::DeleteFile

Summary:
DestroyDB that is used in tests loops over the files returned by ::GetChildren and delete them one by one. Such files might be already deleted in the file system (during DeleteObsoleteFileImpl for example) but will get actually deleted with a delay sometimes before ::DeleteFile is called on the file name. We have some test failures where FaultInjectionTestEnv::DeleteFile fails on assert(s.ok()) during DestroyDB. This patch removes the assert statement to fix that.
Closes https://github.com/facebook/rocksdb/pull/3324

Differential Revision: D6659545

Pulled By: maysamyabandeh

fbshipit-source-id: 4c9552fbcd494dcf3e61d475c11fc965c4388b2c

utilities/transactions/transaction_test.h

@@ -72,6 +72,11 @@ class TransactionTest : public ::testing::TestWithParam<
 
   ~TransactionTest() {
     delete db;
+    // This is to skip the assert statement in FaultInjectionTestEnv. There
+    // seems to be a bug in btrfs that the makes readdir return recently
+    // unlink-ed files. By using the default fs we simply ignore errors resulted
+    // from attempting to delete such files in DestroyDB.
+    options.env = Env::Default();
     DestroyDB(dbname, options);
     delete env;
   }