After commit 1825c8d7 ("erofs: force inplace I/O under low
memory scenario") and TRYALLOC is widely used, DELAYEDALLOC won't
be used anymore. Remove related dead code. Also, remove the blank
line at the end of zdata.h.

Link: https://lore.kernel.org/r/20211106082315.25781-1-huyue2@yulong.comReviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Yue Hu <huyue2@yulong.com>
Signed-off-by: Gao Xiang <xiang@kernel.org>