camcontrol(8): remove unnecessary CCB zeroing

After 3e404b8c53d, cam_getccb(3) clears the returned CCB, making
a number of calls to CCB_CLEAR_ALL_EXCEPT_HDR(3) unnecessary.

Reviewed By: imp
Sponsored by: NetApp, Inc.
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D27812