update metric desc (#1376)
update metric desc (#1376)

`spark.executor.memory_used` and `spark.executor.max_memory` have the exact same description, this PR fixes it.
DataDog/integrations-core,DataDog/integrations-core,DataDog/integrations-core,DataDog/integrations-core,DataDog/integrations-core,DataDog/integrations-core,DataDog/integrations-core,DataDog/integrations-core,DataDog/integrations-core,DataDog/integrations-core