[JFFS2] Delete everything related to obsolete JFFS2_PROC option

Delete everything related to the apparently non-existent kernel config
option JFFS2_PROC.

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>