tcpdump: punt duplicate versioned binary

The tcpdump package likes to install two binaries into /usr/sbin --
one named "tcpdump" and one named "tcpdump.<ver>".  But it does this
by installing the file twice rather than using links.  Since the alt
name is useless to us, just punt it.

[Peter: Rework to use POST_INSTALL_TARGET_HOOKS instead]
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>