Don't SIGABORT if device-mapper doesn't generate uevent for DeleteDevice

It looks like in some rare scenarios device-mapper won't create an
uevent while handling DM_DEV_REMOVE ioctl.

Since failure to generate uevent will result in ueventd not cleaning up
/dev paths in user space, it should be ok to just fail DeleteDevice call
without aborting the entire process.

Test: presubmit
Bug: 171266986
Change-Id: Iece28e6e02c35ac4bf33b9be74dfe1bbbb466bd4