This switches ext4 over to the generic support provided in libfs.

Since casefolded dentries behave the same in ext4 and f2fs, we decrease
the maintenance burden by unifying them, and any optimizations will
immediately apply to both.
Signed-off-by: NDaniel Rosenberg <drosen@google.com>
Reviewed-by: NEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20201028050820.1636571-1-drosen@google.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>