output: IPFIX: remove compiler attribute macros

output: IPFIX: remove compiler attribute macros

The ipfix.h header includes three macros which expand to compiler attributes.
Presumably, at some point the definitions were one branch of an if-else
preprocessor conditional where the definitions in the other branch expanded to
nothing.  This is no longer the case.  Only one of the macros (`__packed`) is
used and the raw attribute is used elsewhere in the code-base.  Remove the
macros.

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>