Drop check requirement, we don't do unit tests.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

diff -Nura radvd-2.1.orig/configure.ac radvd-2.1/configure.ac
--- radvd-2.1.orig/configure.ac	2014-07-22 08:23:12.642260069 -0300
+++ radvd-2.1/configure.ac	2014-07-22 08:23:21.270552628 -0300
@@ -49,7 +49,6 @@
 dnl Determine CC and preset CFLAGS
 AC_PROG_CC_C99
 AC_PROG_RANLIB
-PKG_CHECK_MODULES([CHECK], [check >= 0.9.4])
 
 dnl Determine of netlink is available
 AC_MSG_CHECKING(netlink)