Dropped the HASORPHAN scan in lfsr_mount

The motivation here is to simplify lfsr_mount, but there's a number of
knock-on effects.

For one, lfsr_mount should now be faster on filesystems with large
blocks:

  O(nb(log b)(log_b n)) -> O(nb(log_b n))

But we now no longer check if our filesystem contains orphaned
stickynotes or unknown filetypes:

- Orphaned stickynotes turned out to not be a big deal. If we find
  orphans we'd need to do a second traversal to remove them anyways (no
  mutation allowed in lfsr_mount), so this actually ends up a net
  improvement in the found-orphan case.

  If anything, doing a traversal on first write sets user expectations
  correctly, and can be offloaded with lfsr_fs_mkconsistent or
  lfsr_fs_gc.

- Unknown filetypes are a bit more annoying (I actually forgot about
  this check), but unknown filetypes that require special care should
  probably set WCOMPAT/RCOMPAT flags.

  Allowing unknown filetypes is a bit more flexible in cases where a
  filesystem image is being shared between drivers with different
  features (bootloader + app for example).

  Though we should probably add more checks/tests that we're handling
  these correctly now that we no longer just bail during mount...

Also renamed LFS_I_HASORPHANS -> LFS_I_UNTIDY.

Not doing something is cheaper than doing something, so this saves a bit
of code:

           code          stack          ctx
  before: 38120           2624          752
  after:  38020 (-0.3%)   2624 (+0.0%)  752 (+0.0%)

lfs.h

@@ -228,8 +228,7 @@ enum lfs_type {
                         0x00008000  // Filesystem may have uncompacted metadata
 
 // internally used flags, don't use these
-#define LFS_I_HASORPHANS \
-                        0x00001000  // Filesystem may have untracked orphans
+#define LFS_I_UNTIDY    0x00001000  // Filesystem may have orphaned stickynotes
 
 
 // Block types