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/lets_split/keymaps/OLED_sample/config.h

@@ -38,8 +38,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define SSD1306OLED
 //#define OLED_ROTATE180
 
-
-#define PREVENT_STUCK_MODIFIERS
 #define TAPPING_FORCE_HOLD
 #define TAPPING_TERM 100
 

keyboards/lets_split/keymaps/adam/config.h

@@ -43,7 +43,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #undef TAPPING_TERM
 #define TAPPING_TERM 200 //At 500 some bad logic takes hold
-#define PREVENT_STUCK_MODIFIERS
 #define IGNORE_MOD_TAP_INTERRUPT
 #define PERMISSIVE_HOLD
 

keyboards/lets_split/keymaps/khord/config.h

@@ -25,9 +25,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #define TAPPING_TERM 150
 
-/* prevent stuck modifiers */
-#define PREVENT_STUCK_MODIFIERS
-
 /* Use I2C or Serial, not both */
 
 #define USE_SERIAL

keyboards/lets_split/keymaps/piemod/config.h

@@ -43,7 +43,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define RGBLIGHT_EFFECT_KNIGHT_LENGTH 1
 
 // Typing Options
-#define PREVENT_STUCK_MODIFIERS
 #define QMK_KEYS_PER_SCAN 4
 
 #endif

keyboards/lets_split/keymaps/waples/config.h

@@ -12,6 +12,4 @@
 //  #define MASTER_RIGHT
 #define EE_HANDS              // We like to have choices I guess
 
-#define PREVENT_STUCK_MODIFIERS // When switching layers, this will release all mods
-
 #endif

keyboards/lets_split/keymaps/xk/config.h

@@ -37,7 +37,6 @@ the Free Software Foundation, either version 2 of the License, or
 #define EE_HANDS
 
 
-#define PREVENT_STUCK_MODIFIERS
 #define IGNORE_MOD_TAP_INTERRUPT
 #define PERMISSIVE_HOLD