unlink proxy_cache and proxy_cache_valid

src/http/modules/ngx_http_proxy_module.c

diff --git a/src/http/modules/ngx_http_proxy_module.c b/src/http/modules/ngx_http_proxy_module.c
index 680d77a..1338476 100644
--- a/src/http/modules/ngx_http_proxy_module.c
+++ b/src/http/modules/ngx_http_proxy_module.c
@@ -2068,10 +2068,6 @@
     ngx_conf_merge_ptr_value(conf->upstream.cache_valid,
                              prev->upstream.cache_valid, NULL);
 
-    if (conf->upstream.cache_valid == NULL) {
-        conf->upstream.cache = NULL;
-    }
-
 #endif
 
     if (conf->method.len == 0) {