clean up nginx cache specific code

docker/nginx/conf.d/include/location-skylink

@@ -25,6 +25,8 @@ set $skynet_proof '';
 set $limit_rate 0;
 
 access_by_lua_block {
+    -- the block below only makes sense if we are using nginx cache
+    if not ngx.var.skyd_disk_cache_enabled then
         local httpc = require("resty.http").new()
 
         -- detect whether requested skylink is v2
@@ -61,6 +63,7 @@ access_by_lua_block {
         if ngx.shared.nocache:get(ngx.var.skylink_v1) then
             ngx.var.nocache = "1"
         end
+    end
 
     if require("skynet.account").accounts_enabled() then
         -- check if portal is in authenticated only mode
@@ -85,6 +88,8 @@ header_filter_by_lua_block {
     ngx.header["Skynet-Portal-Api"] = ngx.var.scheme .. "://" .. os.getenv("PORTAL_DOMAIN")
     ngx.header["Skynet-Server-Api"] = ngx.var.scheme .. "://" .. os.getenv("SERVER_DOMAIN")
 
+    -- the block below only makes sense if we are using nginx cache
+    if not ngx.var.skyd_disk_cache_enabled then
         -- not empty skynet_proof means this is a skylink v2 request
         -- so we should replace the Skynet-Proof header with the one
         -- we got from /skynet/resolve/ endpoint, otherwise we would
@@ -98,6 +103,7 @@ header_filter_by_lua_block {
         if ngx.header["Content-Length"] and tonumber(ngx.header["Content-Length"]) > 1e+9 then
             ngx.shared.nocache:set(ngx.var.skylink_v1, ngx.header["Content-Length"])
         end
+    end
 }
 
 limit_rate_after 512k;