staging: exfat: remove two unused functions

staging: exfat: remove two unused functions

Fix sparse warnings:

drivers/staging/exfat/exfat_core.c:2045:4: warning: symbol 'calc_checksum_1byte' was not declared. Should it be static?
drivers/staging/exfat/exfat_core.c:2080:5: warning: symbol 'calc_checksum_4byte' was not declared. Should it be static?

The two functions has no caller in tree, so remove it.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20191114140348.46088-1-yuehaibing@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>