SSL: silenced warnings when building with OpenSSL 3.0.

The OPENSSL_SUPPRESS_DEPRECATED macro is used to suppress deprecation warnings.
This covers Session Tickets keys, SSL Engine, DH low level API for DHE ciphers.

Unlike OPENSSL_API_COMPAT, it works well with OpenSSL built with no-deprecated.
In particular, it doesn't unhide various macros in OpenSSL includes, which are
meant to be hidden under OPENSSL_NO_DEPRECATED.

src/event/ngx_event_openssl.h

diff --git a/src/event/ngx_event_openssl.h b/src/event/ngx_event_openssl.h
index a54a86a..81b87d7 100644
--- a/src/event/ngx_event_openssl.h
+++ b/src/event/ngx_event_openssl.h
@@ -12,6 +12,8 @@
 #include <ngx_config.h>
 #include <ngx_core.h>
 
+#define OPENSSL_SUPPRESS_DEPRECATED
+
 #include <openssl/ssl.h>
 #include <openssl/err.h>
 #include <openssl/bn.h>