Whoops.

This allows us to os.listdir("/").

We attempt to share st3m with the recovery firmware, and thus must
eliminate two components that can't live in the recovery firmware:

1. The startup function, which contains references to all matters of
   subfunctionality we don't want (audio, micropython, etc)
2. The FS code, which contains references to the tarball extraction
   logic (which we don't want to embed into recovery mode either).

Whoops, this shouldn't have happened. Sorry.

Previously MicroPython would mount LittleFS directly from the partition
by itself, using its own VFS stack.

This reconfigured the VFS layer in MicroPython to use POSIX
open/read/write/etc calls, which are backed by ESP-IDF. Now, instead of
managing (possibly multuple) block devices at different mountpoints,
MicroPython simply passes through all VFS access to the ESP-IDF VFS.

Then, we make the ESP-IDF VFS mount a wear-leveled FAT (backed by the
same partition which previously held LittleFS) onto /.