Removed implicit enabling of multilib support from x86-64 architecture

- To be able to build "pure" x86-64 systems (non-multilib) we need to remove
  this hardwired multilib by default behavior from the x86-64 architecture
  configuration.

architecture/x86-64/config.in

@@ -26,6 +26,3 @@ choice SDECFG_X8664_OPT generic   \
 if [ $SDECFG_X8664_OPT != generic ] ; then
 	SDECFG_ID="$SDECFG_ID-$SDECFG_X8664_OPT"
 fi
-
-SDECFGSET_MULTILIB=1
-