m68k: apollo, q40, sun3, sun3x: Remove arch_gettimeoffset implementations

These dummy implementations are no better than
default_arch_gettimeoffset() so remove them.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>