Revert "configure: Check for major() more strictly"

This reverts commit d53fa838,
which is no longer needed now that gnulib does the job.
Signed-off-by: NEric Blake <eblake@redhat.com>

configure.ac

@@ -144,10 +144,7 @@ AC_TYPE_UID_T
 dnl Support building Win32 DLLs (must appear *before* AM_PROG_LIBTOOL)
 AC_LIBTOOL_WIN32_DLL
 
-old_CFLAGS=$CFLAGS
-CFLAGS="$CFLAGS -Werror"
 AC_HEADER_MAJOR
-CFLAGS=$old_CFLAGS
 
 m4_ifndef([LT_INIT], [
   AM_PROG_LIBTOOL