voxel: delete voxel_npcx797fc switch variant
the only support CHIP_VARIANT npcx797fc ec chip
BRANCH=master
TEST=make buildall, workable on the re-worked Board.
CHIP:=npcx
CHIP_FAMILY:=npcx7
-# A limited Voxe boards are reworked with NPCX797FC variant. Set the
-# modify the variant type to match.
-ifeq ($(BOARD),voxel_npcx797fc)
CHIP_VARIANT:=npcx7m7fc
-else
-CHIP_VARIANT:=npcx7m6fc
-endif
BASEBOARD:=volteer
board-y=board.o
