cfdisk: shorten the help screen to make it fit within 25 lines

cfdisk: shorten the help screen to make it fit within 25 lines

When the terminal has less than 32 lines, the new cfdisk ignored the
fact that the help-screen text was longer and just skipped printing
the remaining lines.  Instead of introducing a minipager for the help
screen, just condense its text and remove unneeded lines.  Now the
text occupies just 25 lines, which should fit on most terminals.

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>