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/xd75/keymaps/davidrambo/config.h

@@ -20,7 +20,6 @@
 #include "../../config.h"
 
 #define TAPPING_TERM 200
-#define PERMISSIVE_HOLD 
-#define PREVENT_STUCK_MODIFIERS
+#define PERMISSIVE_HOLD
 
 #endif

keyboards/xd75/keymaps/tdl-jturner/config.h

@@ -26,7 +26,6 @@
 #define TAPPING_TOGGLE 2
 //#define PERMISSIVE_HOLD
 //#define QMK_KEYS_PER_SCAN 4
-#define PREVENT_STUCK_MODIFIERS
 #define FORCE_NKRO
 
 #define MOUSEKEY_INTERVAL 16