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/contra/keymaps/ryanm101/config.h

@@ -3,7 +3,6 @@
 
 #include "config_common.h"
 
-#define PREVENT_STUCK_MODIFIERS
 #define TAPPING_TERM 200
 
 #ifdef AUDIO_ENABLE
@@ -28,7 +27,7 @@
 /* enable basic MIDI features:
    - MIDI notes can be sent when in Music mode is on
 */
-                                
+
 #define MIDI_BASIC
 
 /* enable advanced MIDI features:
@@ -42,4 +41,4 @@
 /* override number of MIDI tone keycodes (each octave adds 12 keycodes and allocates 12 bytes) */
 //#define MIDI_TONE_KEYCODE_OCTAVES 2
 
-#endif
+#endif