bug#54112: dd seek_bytes etc. is confusing

[Paul Eggert]

While looking into Bug#45648 I noticed that the GNU extensions 
count_bytes, seek_bytes, and skip_bytes are confusing, and the proposed 
fix to bug#45648 would make them even more confusing. To fix this 
confusion, we should deprecate these options, and instead say that if 
you want to use byte counts you should use a number string ending in "B".

Here's another way to put it.  Currently this:

   dd oseek=100KiB

means "seek 102,400 blocks". It should simply mean "seek 102,400 bytes", 
which is what it says. And if we change oseek's meaning this way, we 
don't need "oseek_bytes".

Although this is an incompatible change to GNU dd, I don't think it'll 
affect real-world uses (who would use oseek in such a confusing way 
now?) and overall it will be a win.