diffutils has a rather confused set of getext macros with different names and
strange conflicting version requirements. This patch removes the problematic
macros allowing it to 'gettextize' to the latest standard gettext code without
issue.
(From OE-Core rev: a40b89333652ca22a6e6957ab8a2a4e41b87b4c0)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>