omap3_beagle: remove JFFS2 support.

We do not use JFFS2 by default and it conflicts with
CONFIG_CMD_FS_GENERIC (ls command is the same). Since most of our
BOOTCMD can be simplified by using the FS_GENERIC, dropping JFFS2

Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Joel Fernandes <joelf@ti.com>