Cut deducible template arg in DefaultKeepAliveExecutor init
Cut deducible template arg in DefaultKeepAliveExecutor init

Summary: [Folly] Cut deducible template arg in `DefaultKeepAliveExecutor` init - let it be deduced instead.

Reviewed By: andriigrynenko

Differential Revision: D14236171

fbshipit-source-id: 2de043efe541c13c59764715516b08d77efcb99b

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly