GCC4.6: Drop dead code from yaffs_guts.c

Drop yaffs_DeleteWorker():
yaffs_guts.c:1556:12: warning: 'yaffs_DeleteWorker' defined but not used

Drop yaffs_VerifyTnodeWorker():
yaffs_guts.c:600:12: warning: 'yaffs_VerifyTnodeWorker' defined but not used

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Mike Frysinger <vapier@gentoo.org>