Make PREVENT_STUCK_MODIFIERS the default (#3107)

* Remove chording as it is not documented, not used, and needs work.

* Make Leader Key an optional feature.

* Switch from `PREVENT_STUCK_MODIFIERS` to `STRICT_LAYER_RELEASE`

* Remove `#define PREVENT_STUCK_MODIFIERS` from keymaps.

keyboards/handwired/dactyl/config.h

@@ -63,8 +63,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 /* Set 0 if debouncing isn't needed */
 #define DEBOUNCE    15
 
-#define PREVENT_STUCK_MODIFIERS
-
 #define USB_MAX_POWER_CONSUMPTION 500
 
 #endif