fix(rgb48_lightstring): move color_mode to effect

With no rgbhsv datapoint, this device only supports one valid color mode, which is implied
by the available dps so color_mode is not needed.

"colour" is used by the device when in "drawing" or "painting" mode, which should be an effect rather
than the "hs" color mode since there is no direct hsv control.

Alternative to PR #5591 which only replaced the name for "colour", leaving only one actual color mode in the list, but left it as color_mode, relying on fallback to effect.

custom_components/tuya_local/devices/rgb48_lightstring.yaml

@@ -34,18 +34,17 @@ entities:
         name: switch
       - id: 21
         type: string
-        name: color_mode
+        name: effect
         mapping:
           - dps_val: "white"
-            value: "color_temp"
+            value: "off"
           - dps_val: "colour"
-            value: "hs"
-            hidden: true  # there is no RGB dp, so prevent selection of this
+            value: "draw"
           - dps_val: "scene"
             value: "scene"
           - dps_val: "music"
             value: "music"
-            hidden: true
+            hidden: true  # No music dps
       - id: 22
         type: integer
         name: brightness