Use skiplist rep for range tombstone memtable

Summary: somehow missed committing this update in D62217

Test Plan: make check

Reviewers: sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D65361

db/db_properties_test.cc

@@ -558,7 +558,7 @@ TEST_F(DBPropertiesTest, NumImmutableMemTable) {
     ASSERT_TRUE(dbfull()->GetProperty(
         handles_[1], "rocksdb.cur-size-active-mem-table", &num));
     // "384" is the size of the metadata of two empty skiplists, this would
-    // break if we change the default vectorrep/skiplist implementation
+    // break if we change the default skiplist implementation
     ASSERT_EQ(num, "384");
 
     uint64_t int_num;

db/memtable.cc

@@ -68,7 +68,7 @@ MemTable::MemTable(const InternalKeyComparator& cmp,
       table_(ioptions.memtable_factory->CreateMemTableRep(
           comparator_, &allocator_, ioptions.prefix_extractor,
           ioptions.info_log)),
-      range_del_table_(ioptions.memtable_factory->CreateMemTableRep(
+      range_del_table_(SkipListFactory().CreateMemTableRep(
           comparator_, &allocator_, nullptr /* transform */,
           ioptions.info_log)),
       data_size_(0),