refactor(pubsub): simpify the get_cmd implementation (#8608)

apisix/core/pubsub.lua

@@ -26,7 +26,6 @@ local pb           = require("pb")
 local ngx          = ngx
 local setmetatable = setmetatable
 local pcall        = pcall
-local pairs        = pairs
 
 
 local _M = { version = 0.1 }
@@ -57,15 +56,10 @@ end
 
 -- parse command name and parameters from client message
 local function get_cmd(data)
-    for key, value in pairs(data) do
-        -- There are sequence and command properties in the data,
-        -- select the handler according to the command value.
-        if key ~= "sequence" and key ~= "req" then
-            -- new version of lua-protobuf will add a new field 'oneof_name = oneof_type'
-            -- so we also need to filter it out (in this case, the 'req' key)
-            return key, value
-        end
-    end
+    -- There are sequence and command properties in the data,
+    -- select the handler according to the command value.
+    local key = data.req
+    return key, data[key]
 end