jbd2: remove debug dependency on debug_fs and update Kconfig help text

Commit b6e96d00 ("jbd2: use module parameters instead of debugfs
for jbd_debug") removed any need for a dependency on DEBUG_FS.  It
also moved the /sys variables out from underneath the typical debugfs
mount point.  Delete the dependency and update the /sys path to where
the debug settings are currently.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>