Remove an empty #if block.

The interesting thing is that looking through Darren's commit logs,
the line containing an extern ppsratecheck() definition was removed
from the v5-1-RELEASE branch but not from HEAD (I have taken his
CVS tree and converted it to GIT). There is a commit adding an
additional #if defined to the empty block. I can only assume that
this was intentional for something later. Looking through HEAD the
extern ppsratecheck() is there. However if we put it back it would
conflict with a static ppsratecheck() definition in fil.c when
building ipftest.

Therefore we remove this empty block.

ppsratecheck() is a function in the FreeBSD kernel. However ipftest
cannot call the ppsratecheck() in the kernel. Therefore one exists in
fil.c for use when building the userland ipftest utility which
approximates the packet filter in userland for testing of ipfilter
rules against packets captured with tcpdump.

MFC after: 1 week