Cleaned up dependent fixes on branch

These should probably have been cleaned up in each commit to allow
cherry-picking, but due to time I haven't been able to.

- Went with creating an mdir copy in lfs_dir_commit. This handles a
  number of related cleanup issues in lfs_dir_compact and it does so
  more robustly. As a plus we can use the copy to update dependencies
  in the mlist.

- Eliminated code left by the ENOSPC file outlining

- Cleaned up TODOs and lingering comments

- Changed the reentrant many directory create/rename/remove test to use
  a smaller set of directories because of space issues when
  READ/PROG_SIZE=512

tests/test_dirs.toml

@@ -155,7 +155,7 @@ code = '''
 '''
 
 [[case]] # reentrant many directory creation/rename/removal
-define.N = [5, 10] # TODO changed from 20, should we be able to do more?
+define.N = [5, 11]
 reentrant = true
 code = '''
     err = lfs_mount(&lfs, &cfg);

tests/test_exhaustion.toml

@@ -338,7 +338,6 @@ exhausted:
 define.LFS_ERASE_CYCLES = 0xffffffff
 define.LFS_BLOCK_COUNT = 256 # small bd so test runs faster
 define.LFS_BLOCK_CYCLES = [5, 4, 3, 2, 1]
-#define.LFS_BLOCK_CYCLES = [4, 2]
 define.CYCLES = 100
 define.FILES = 10
 code = '''