build: remove call to AC_PROG_GCC_TRADITIONAL libevent requires Autoconf 2.67+, and from atleast this version onwards, if not earlier, this macro is obsolescent. > This macro is obsolescent, since current versions of the GNU > C compiler fix the header files automatically when installed. See: https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.67/autoconf.html#AC_005fPROG_005fGCC_005fTRADITIONAL.