video: fbdev: atari: Remove backward bug-compatibility

As of v2.1.0, falcon_decode_var() contains a quirk to fix a rounding
error, as explained by Günther Kelleter on Fri, 30 Aug 1996:

    This diff removes the now obsolete Falcon video option "pwrsave", and
    fixes a rounding error that is triggered by the resolution switching X
    server (those who use the pixel clock value 39722 in their /etc/fb.modes
    should change it to 39721).

However, this causes the modified video mode returned by
falcon_decode_var() to not match the video mode returned by
falcon_encode_var().  Fix this by dropping the quirk.

Unfortunately /etc/fb.modes in fbset was never updated, so the
"640x480-60" mode still contains the wrong pixclock.
Hence this change may introduce a regression.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>