sstate-cache-management.sh: fix remove duplicate failed when multiple archs
The implementation of `--remove-duplicated' has been modified by the commit:
http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=
0740f82aea92da0195524e37c372f9981e7f5e6d
In above commit, sstate cache files with multiple archs are not considered
duplicate and don't need to be removed as duplicated any more.
Update the description of `--remove-duplicated' in usage to keep consistent
with implementation.
[YOCTO #3635]
Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
