ext4: allow verity with fs block size < PAGE_SIZE

Now that the needed changes have been made to fs/buffer.c, ext4 is ready
to support the verity feature when the filesystem block size is less
than the page size.  So remove the mount-time check that prevented this.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Tested-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20221223203638.41293-12-ebiggers@kernel.org