m68k: remove useless file m68k-qreg.h

Unused since:

    commit e1f3808e
    Author: pbrook <pbrook@c046a42c-6fe2-441c-8c8c-71466251a162>
    Date:   Sat May 24 22:29:16 2008 +0000

        Convert m68k target to TCG.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Thomas Huth <huth@tuxfamily.org>