kbscan: Remove unused array

Signed-off-by: Tim Crawford <tcrawford@system76.com>

src/board/system76/common/kbscan.c

@@ -279,7 +279,6 @@ void kbscan_event(void) {
     static uint8_t kbscan_layer = 0;
     uint8_t layer = kbscan_layer;
     static uint8_t kbscan_last_layer[KM_OUT][KM_IN] = { { 0 } };
-    static bool kbscan_ghost[KM_OUT] = { false };
     uint8_t matrix_curr[KM_OUT];
 
     static bool debounce = false;