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

[jhb]

Summary

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

[imp]

leaving aside question of 'why do we still need these drivers', these change are good.

[emaste]

In D34795#788641, @imp wrote:

leaving aside question of 'why do we still need these drivers', these change are good.

Perhaps we'll sort that out in D23928, eventually. They might get removed with a final spl* cleanup.