When using Universal Compaction, Zero out seqID in the last file too

Summary: I didn't figure out the reason why the feature of zeroing out earlier sequence ID is disabled in universal compaction. I do see bottommost_level is set correctly. It should simply work if we remove the constraint of universal compaction.

Test Plan: make all check

Reviewers: haobo, dhruba, kailiu, igor

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D15423

db/db_impl.cc

@@ -2507,8 +2507,7 @@ Status DBImpl::DoCompactionWork(CompactionState* compact,
         // If this is the bottommost level (no files in lower levels)
         // and the earliest snapshot is larger than this seqno
         // then we can squash the seqno to zero.
-        if (options_.compaction_style == kCompactionStyleLevel &&
-            bottommost_level && ikey.sequence < earliest_snapshot &&
+        if (bottommost_level && ikey.sequence < earliest_snapshot &&
             ikey.type != kTypeMerge) {
           assert(ikey.type != kTypeDeletion);
           // make a copy because updating in place would cause problems