FI_DROP_CACHE was introduced in commit 1e84371ffeef ("f2fs: change atomic and volatile write policies") for volatile write feature, after commit 7bc155fec5b3 ("f2fs: kill volatile write support"), we won't support volatile write, let's delete related codes. Signed-off-by: Chao Yu <chao@kernel.org> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>