sstable: clean up; drop support for range deletion v1 blocks

[jbowens]

sstable/rowblk: replace RawWriter with methods on rowblk.Writer

sstable: add metaIndexWriter

Add a helper metaIndexWriter type that handles sorting the meta index keys so Writer.Close doesn't need to maintain a delicate ordering.

sstable: drop support for v1 range deletion blocks

The v1 range deletion blocks predate Pebble. Our format major versions that required compaction of all pre-Pebble sstables ensure that no v1 range deletion blocks should exist in the wild without an accompanying v2 range deletion block. This required regeneration of the sstable fixtures.

sstable: add layoutWriter

Refactor management of block handles, file size and the meta index into a layoutWriter type responsible for writing blocks to durable storage. This will allow the columnar block format to share logic.

[cockroach-teamcity]

This change is 

[RaduBerinde]

Is this true even of older backups? (CC @dt) I remember trying to deprecate some table formats before and I ended up reverting it because of backup.