Inline RGB config, remove snippet

RGB settings moved from snippets/rgb-config into corne.conf.
Snippet dir + snippet_root + build.yaml snippet refs removed.

build.yaml

@@ -5,12 +5,10 @@ include:
   - board: nice_nano_v2
     shield: corne_left nice_oled
     artifact-name: nice_corne_left_oled_rgb
-    snippet: rgb-config
   - board: nice_nano_v2
     shield: corne_right nice_oled
     cmake-args: -DCONFIG_NICE_OLED_WIDGET_ANIMATION_PERIPHERAL_CAT=n -DCONFIG_NICE_OLED_WIDGET_ANIMATION_PERIPHERAL_KM=y
     artifact-name: nice_corne_right_oled_rgb
-    snippet: rgb-config
   ### CORNE END ###
 
   ### SETTINGS_RESET START ###