config: Remove deprecated macro from FreeBSD configuration files

The macro STDLIB_HAS_MALLOC_PROTOS was deprecated in commit
daff4006627fc88be85dade3d72aa45e57a6804a.

Change-Id: I9c2129f6f3d5be6a00ef6ddd358967e0fd4f7ec9
Reviewed-on: http://gerrit.openafs.org/11333
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Garrett Wollman <wollman@csail.mit.edu>
Reviewed-by: D Brashear <shadow@your-file-system.com>