erofs: remove a void EROFS_VERSION macro set in Makefile

erofs: remove a void EROFS_VERSION macro set in Makefile

Since commit 4f761fa253b4 ("erofs: rename errln/infoln/debugln to
erofs_{err, info, dbg}") the defined macro EROFS_VERSION has no affect,
therefore removing it from the Makefile is a non-functional change.

Link: https://lore.kernel.org/r/20201030122839.25431-1-vladimir@tuxera.com
Reviewed-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Vladimir Zapolskiy <vladimir@tuxera.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>