kernel/multiboot2: Remove glbl_core_data variable
kernel/multiboot2: Remove glbl_core_data variable

It has been renamed to armv8_glbl_core_data and is in armv8/init.c now.

Signed-off-by: Moritz Hoffmann <53ba0aa052d551db5cb133c62d34e71044d0deba@inf.ethz.ch>

BarrelfishOS/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish