Previously, kvm_read was used to get the memory usage in FreeBSD. However,
this has been deprecated in favor of sysctl. This patch implements this
change.
Some work had previously been done in this direction, as could be seen in
the file src/mem_freebsd_sysctl.c. Since this file is no longer needed, it
has been removed.
Additionally, some formatting has been done on the remaining older code for
a more consistent style.
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