metric currently_open_for_writing, used to inform # of sstables opened for writing,
holds the same value as total_open_for_writing. that means we aren't actually
decreasing the counter, so it is bogus.
Moved to sstable_writer, because sstable is used by writer to open files,
which are then extracted from sstable object, and later the same object is
reused for read-only mode.
Fixes#9455.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20211013134812.177398-1-raphaelsc@scylladb.com>