CLEANUP: ssl: remove ifdef around SSL_CTX_get_extra_chain_certs()

Instead define this one in openssl-compat.h when
SSL_CTRL_GET_EXTRA_CHAIN_CERTS is not defined (which was the current
condition used in the ifdef).
diff --git a/include/common/openssl-compat.h b/include/common/openssl-compat.h
index fb88884..ca171cd 100644
--- a/include/common/openssl-compat.h
+++ b/include/common/openssl-compat.h
@@ -292,5 +292,9 @@
 #define SSL_OP_PRIORITIZE_CHACHA 0
 #endif
 
+#ifndef SSL_CTRL_GET_EXTRA_CHAIN_CERTS
+#define SSL_CTX_get_extra_chain_certs(ctx, chain) do { *(chain) = (ctx)->extra_certs; } while (0)
+#endif
+
 #endif /* USE_OPENSSL */
 #endif /* _COMMON_OPENSSL_COMPAT_H */