Revert "Add an option (disable by default) for removing -fhardened. Show warning cc1plus: warning: ‘_FORTIFY_SOURCE’ is not enabled by ‘-fhardened’ because optimizations are turned off [-Whardened]"

This reverts commit cba72a62eeb485e63fb5ac3d0c4afde68fc7699d.

We always want -fhardened in mimetreeparser, the warning needs to be
fixed properly in extra-cmake-module not here.