HAMMER 43C/Many: Performance cleanup

HAMMER 43C/Many: Performance cleanup

* Do not put an inode on the sync list when it becomes inactive, unless
  it no longer has filesystem visibility.  This greatly reduces the amount
  of cycling which occurs on the inode B-Tree element, and greatly reduces
  spurious backend flushes.

  This change results in a major performance improvement for both reads
  and writes in a massively parallel I/O test (blogbench).  Write
  performance more then doubles and read performance increases by 20%.

* Lock the freemap free code.

* Remove some of the debug code.