tell the kernel to forget about a partition
delpart device partition
delpart asks the Linux kernel to forget about the specified partition (a number) on the specified device. The command is a simple wrapper around the "del partition" ioctl.
This command doesn't manipulate partitions on a block device.
The delpart command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/.