[docs] Cleanup custom colors declaration logic

docs/src/docs/theming/colors.mdx

@@ -124,20 +124,9 @@ separated with `.`, for example `pink.3`:
 
 ## Add custom colors types
 
-TypeScript will only autocomplete Mantine's default colors when accessing the theme. To add your custom colors to the MantineColor type, you can use TypeScript module declaration:
+TypeScript will only autocomplete Mantine's default colors when accessing the theme. To add your custom colors to the MantineColor type, you can use TypeScript module declaration.
 
 ```ts
-import { Tuple } from '@mantine/core';
-
-type CustomColors = 'primaryColorName' | 'secondaryColorName';
-
-declare module '@mantine/core' {
-  export interface MantineThemeColorsOverride {
-    colors: Record<CustomColors, Tuple<string, 10>>;
-  }
-}
-
-// or if you want to "extend" standard colors
 import { Tuple, DefaultMantineColor } from '@mantine/core';
 
 type ExtendedCustomColors = 'primaryColorName' | 'secondaryColorName' | DefaultMantineColor;