ce,cp: Remove pointless checks for <sys/cdefs.h>

Both of these headers check for _SYS_CDEFS_H_ after including
<sys/param.h> which itself includes <sys/cdefs.h>.

PR: 263102 (exp-run)
Reviewed by: brooks, imp, emaste
Differential Revision: https://reviews.freebsd.org/D34795

(cherry picked from commit 17554af4e8531f443fce1a58ab6d4b45d82af5f2)