As flat mutation reader {up,down}grades get added to the write path,
comparing range-tombstone-containing (at least) sstables byte-by-byte
to a reference is starting to seem like a fool's errand.
* When a flat mutation reader is {up,down}graded, information may get
lost while splitting range tombstones. Making those splits revertable
should in theory be possible but would surely make {up,down}graders
slower and more complex, and may also possibly entail adding
information to in-memory representation of range tombstones and
range rombstone changes. Such investment for the sake of 7 unit tests
does not seem wise, given that the plan is to get rid of reader
{up,down}grade logic once the move to flat mutation reader v2 is
completed.
* All affected tests also validate their written sstables
semantically.
* At least some of the offending reference sstables are not
"canonical" wrt range tombstones to begin with -- they contain range
tombstones that overlap with clustering rows. The fact that Scylla
does not "canonicalize" those in some way seems purely incidental.
Signed-off-by: Michael Livshin <michael.livshin@scylladb.com>