FROMLIST: ext4: Use generic casefolding support

This switches ext4 over to the generic support provided in
commit 65832afbeaaf ("fs: Add standard casefolding support")

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Test: Boots, /data/media is case insensitive
Bug: 138322712
Link: https://lore.kernel.org/linux-f2fs-devel/20200208013552.241832-1-drosen@google.com/T/#t
Change-Id: I3a0705278100590df4c7cdd0dcdf945e9f11feb7