Revert: "f2fs: check in-memory sit version bitmap"

Revert: "f2fs: check in-memory sit version bitmap"

Commit ae27d62e6bef ("f2fs: check in-memory sit version bitmap") added
a mirror for sit version bitmap, it expects to detect in-memory
corruption, however we never got any reports from the check points
for almost decade, let's remove the code, it can help to save
memories.

Cc: wallentx <william.allentx@gmail.com>
Suggested-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>