mkfs.minix: remove unuseful code

mkfs.minix: remove unuseful code

Checks about inodes vs block sizes does not add much robustness.  Both
values are derived at compilation time from struct minix_inode size, and
they form full definition circle.

Bad block check for none-block devices should not be supressed, user
requested it so let him have it.

Check for st_rdev == 0x0300 || st_rdev == 0x0340 was unreachable.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>