Revert "sstables: Fix incorrect calculation of Compaction Backlog"
Revert "sstables: Fix incorrect calculation of Compaction Backlog"

This reverts commit 458ef4bb066f12c26902da7bc066cc346b86a44b. According
to Glauber Costa:

"It may give us the illusion that fixes something for a particular case
 but this fix is wrong.

 I am trying to help Raphael figure out why the backlog is wrong but
 this patch is not the answer."

avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla