Remove redundant -Wformat -Wformat-security CFLAGS

When configuring with --enable-gcc-warnings, we use -Wformat=2 which
automatically enables the available -Wformat switches, so adding them
again in the --enable-gcc-hardening case doesn't make sense..

configure.in

@@ -98,7 +98,7 @@ AC_ARG_ENABLE(gcc-hardening,
      AS_HELP_STRING(--enable-gcc-hardening, enable compiler security checks),
 [if test x$enableval = xyes; then
     CFLAGS="$CFLAGS -D_FORTIFY_SOURCE=2 -fstack-protector-all"
-    CFLAGS="$CFLAGS -fwrapv -fPIE -Wstack-protector -Wformat -Wformat-security"
+    CFLAGS="$CFLAGS -fwrapv -fPIE -Wstack-protector"
     CFLAGS="$CFLAGS -Wpointer-sign --param ssp-buffer-size=1"
     LDFLAGS="$LDFLAGS -pie"
 fi])