Remove useless -D_ENDIAN from MPE/iX-gcc config

Reviewed-by: NAndy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5564)

Configurations/10-main.conf

@@ -602,7 +602,7 @@ my %targets = (
         inherit_from     => [ "BASE_unix" ],
         CC               => "gcc",
         CFLAGS           => "-O3",
-        cppflags         => "-D_ENDIAN -DBN_DIV2W -D_POSIX_SOURCE -D_SOCKET_SOURCE",
+        cppflags         => "-DBN_DIV2W -D_POSIX_SOURCE -D_SOCKET_SOURCE",
         includes         => add("/SYSLOG/PUB"),
         sys_id           => "MPE",
         lflags           => add("-L/SYSLOG/PUB"),