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/planck/keymaps/steno/config.h

@@ -15,8 +15,6 @@
 
 #define MUSIC_MASK (keycode != KC_NO)
 
-#define PREVENT_STUCK_MODIFIERS
-
 /*
  * MIDI options
  */
@@ -41,4 +39,4 @@
 /* override number of MIDI tone keycodes (each octave adds 12 keycodes and allocates 12 bytes) */
 //#define MIDI_TONE_KEYCODE_OCTAVES 2
 
-#endif
+#endif