ENGINESDIR: document that this configuration is deprecated.

Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/12226)

doc/man3/OpenSSL_version.pod

@@ -120,7 +120,8 @@ if available, or C<OPENSSLDIR: N/A> otherwise.
 =item OPENSSL_ENGINES_DIR
 
 The B<ENGINESDIR> setting of the library build in the form C<ENGINESDIR: "...">
-if available, or C<ENGINESDIR: N/A> otherwise.
+if available, or C<ENGINESDIR: N/A> otherwise. This option is deprecated in
+OpenSSL 3.0.
 
 =item OPENSSL_MODULES_DIR