Fix minor bug in layer deactivation

There was a call to `memmove()` call that shifted one extra byte of memory
whenever a layer was deactivated.  I don't think that `memmove()` would actually
overwrite the source byte, so it shouldn't have any visible effect, but this is
more correct.

Signed-off-by: Michael Richters <gedankenexperimenter@gmail.com>

src/kaleidoscope/layers.cpp

@@ -219,7 +219,7 @@ void Layer_::deactivate(uint8_t layer) {
   // above it down to fill in the gap
   for (uint8_t i = 0; i < active_layer_count_; ++i) {
     if (active_layers_[i] == layer) {
-      memmove(&active_layers_[i], &active_layers_[i + 1], active_layer_count_ - i);
+      memmove(&active_layers_[i], &active_layers_[i + 1], active_layer_count_ - (i + 1));
       --active_layer_count_;
       break;
     }