Remove invalid assertion in compaction_picker_universal.cc (#7421)

Summary:
The assertion checks that there is no overlap in sequence numbers across levels in universal compaction. However, this assumption doesn't hold when there is a delete triggered compaction or a trivial move, as they operate on a subset of a level.

Tests -
make check

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7421

Reviewed By: ajkr

Differential Revision: D23872672

Pulled By: anand1976

fbshipit-source-id: c386deab8e01a5746ca996ff1f4ebcae3b15b7d2

db/compaction/compaction_picker_universal.cc

@@ -461,7 +461,6 @@ Compaction* UniversalCompactionBuilder::PickCompaction() {
 
 // validate that all the chosen files of L0 are non overlapping in time
 #ifndef NDEBUG
-  SequenceNumber prev_smallest_seqno = 0U;
   bool is_first = true;
 
   size_t level_index = 0U;
@@ -471,7 +470,6 @@ Compaction* UniversalCompactionBuilder::PickCompaction() {
       if (is_first) {
         is_first = false;
       }
-      prev_smallest_seqno = f->fd.smallest_seqno;
     }
     level_index = 1U;
   }
@@ -483,16 +481,7 @@ Compaction* UniversalCompactionBuilder::PickCompaction() {
                               &largest_seqno);
       if (is_first) {
         is_first = false;
-      } else if (prev_smallest_seqno > 0) {
-        // A level is considered as the bottommost level if there are
-        // no files in higher levels or if files in higher levels do
-        // not overlap with the files being compacted. Sequence numbers
-        // of files in bottommost level can be set to 0 to help
-        // compression. As a result, the following assert may not hold
-        // if the prev_smallest_seqno is 0.
-        assert(prev_smallest_seqno > largest_seqno);
       }
-      prev_smallest_seqno = smallest_seqno;
     }
   }
 #endif