There is nothing really that fundamentally ties the estimated histogram to
sstables. This patch gets rid of the few incidental ties. They are:
- the namespace name, which is now moved to utils. Users inside sstables/
now need to add a namespace prefix, while the ones outside have to change
it to the right one
- sstables::merge, which has a very non-descriptive name to begin with, is
changed to a more descriptive name that can live inside utils/
- the disk_types.hh include has to be removed - but it had no reason to be
here in the first place.
Todo, is to actually move the file outside sstables/. That is done in a separate
step for clarity.
Signed-off-by: Glauber Costa <glauber@scylladb.com>