Administration: Remove unused font-weight tokens.

Remove the unused `$font-weight-regular` and `$font-weight-medium` Sass
variables from the admin color scheme tokens. Neither variable has a
consumer, so this does not change any generated CSS or runtime styling.

These tokens are also inconsistent with the font weights being introduced
to the Gutenberg project in WordPress 7.1, where new usage should rely on
the new CSS custom properties instead.

Developed in WordPress#12524.

Props ciampo, aduth, tyxla.
Fixes #65629.

git-svn-id: https://develop.svn.wordpress.org/trunk@62755 602fd350-edb4-49c9-b593-d223f7449a82

Author: tyxla

src/wp-admin/css/colors/_tokens.scss

@@ -171,11 +171,6 @@ $line-height-xs: 16px;  // xs
 $line-height-s: 20px;   // s - Most UI elements
 $line-height-m: 24px;   // m - Body large
 
-// Font Weights
-$font-weight-regular: 400;  // Regular - Body text
-$font-weight-medium: 500;   // Medium - Headings, buttons
-
-
 // --------------------------------------------------------------------------
 // Elevation (Box Shadows)
 // --------------------------------------------------------------------------