Fix flex counters logic of converting poll interval to seconds from MS (

sonic-net#878)

According to https://github.com/Azure/SONiC/blob/ec6d35dd2c28491bfade19cfee990fe612f1e5e9/doc/rates-and-utilization/Rates_and_utilization_HLD.md, counterpoll command gives polling interval in milliseconds. 
So when converting them to seconds to be supplied to lua script this should be divide by 1000. However, syncd multiplies it by 1000.

Changed the multiplication to none, and did the converting in lua script - sonic-net/sonic-swss#1855
Fixed issue - sonic-net#8392

syncd/FlexCounter.cpp

@@ -1596,7 +1596,7 @@ void FlexCounter::runPlugins(
     {
         std::to_string(counters_db.getDbId()),
         COUNTERS_TABLE,
-        std::to_string(m_pollInterval * 1000)
+        std::to_string(m_pollInterval)
     };
 
     std::vector<std::string> portList;