ext4: Delete ext4_kvzvalloc()

Since we're not using ext4_kvzalloc(), delete this function.

Signed-off-by: Naoto Kobayashi <naoto.kobayashi4c@gmail.com>
Link: https://lore.kernel.org/r/20191227080523.31808-2-naoto.kobayashi4c@gmail.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>