m68k/Apollo: remove the unused APOLLO_ELPLUS option

Looking at older kernel sources the APOLLO_ELPLUS option was added
somewhere during kernel 2.1, but even kernel 2.2.0 does not contain
any driver that would be enabled through it...

Reported-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>