db: remove unnecessary key clones during ingest load

During ingest loads, the smallest and largest bounds for point and
ranges are calculated. The point and range key bounds are cloned from an
iterator. When setting the overall bounds for the table, the point and /
or range key bounds can be reused for `Smallest` and `Largest`, as the
former are stable.

Remove the unnecessary key clones.

Follow up from cockroachdb#1521.

ingest.go

@@ -202,24 +202,24 @@ func ingestLoad1(
 	switch {
 	case !hasRanges:
 		// Table has only point keys. Use the point key bounds.
-		meta.Smallest = meta.SmallestPointKey.Clone()
-		meta.Largest = meta.LargestPointKey.Clone()
+		meta.Smallest = meta.SmallestPointKey
+		meta.Largest = meta.LargestPointKey
 	case !hasPoints:
 		// Table has only range key. Use the range key bounds.
-		meta.Smallest = meta.SmallestRangeKey.Clone()
-		meta.Largest = meta.LargestRangeKey.Clone()
+		meta.Smallest = meta.SmallestRangeKey
+		meta.Largest = meta.LargestRangeKey
 	default:
 		// Table has both points and ranges. Compute the bounds by considering both
 		// the point and range key bounds.
 		if base.InternalCompare(opts.Comparer.Compare, meta.SmallestPointKey, meta.SmallestRangeKey) < 0 {
-			meta.Smallest = meta.SmallestPointKey.Clone()
+			meta.Smallest = meta.SmallestPointKey
 		} else {
-			meta.Smallest = meta.SmallestRangeKey.Clone()
+			meta.Smallest = meta.SmallestRangeKey
 		}
 		if base.InternalCompare(opts.Comparer.Compare, meta.LargestPointKey, meta.LargestRangeKey) > 0 {
-			meta.Largest = meta.LargestPointKey.Clone()
+			meta.Largest = meta.LargestPointKey
 		} else {
-			meta.Largest = meta.LargestRangeKey.Clone()
+			meta.Largest = meta.LargestRangeKey
 		}
 	}