LU-12373 utils: fix llapi_pcc_del_internal() flags

LU-12373 utils: fix llapi_pcc_del_internal() flags

The pch_flags value used by llapi_pcc_del_internal() was declared
as a "bool" but is used to pass a __u32 flags value from the caller.
This coincidentally works in the case where "flags = 1" (which is
the only value currently in use), but would break in confusing ways
in the future.

Change pch_flags to be "enum lu_pcc_cleanup_flags" to make it clear
what possible flag values are being used in this interface.

Fixes: 871da4898405 ("LU-12373 pcc: uncache the pcc copies when remove a PCC backend")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I41a008856af396376303fb156e2a92bce53ebbe5
Reviewed-on: https://review.whamcloud.com/47123
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Feng, Lei <flei@whamcloud.com>