Import Muriel colours from color-studio package

In https://github.com/Automattic/jetpack/pull/11368 we introduced Muriel colour scheme in Jetpack.

We should import colour variables from `color-studio` dependency instead of adding colours directly in stylesheets:

https://github.com/Automattic/color-studio/blob/013d47d29360509ad0021b186e4a1a12f7f52f93/dist/color-variables.scss

An example in Calypso:
https://github.com/Automattic/wp-calypso/blob/3892cdcb868ca8892f192bb2f19c40db58fbbf1c/assets/stylesheets/shared/_colors.scss#L1-L2

This would ensure less maintenance burden (because of centralised import) and clarity in CSS styles (use of variables).

Search Jetpack stylesheets for the Muriel colour definitions introduced by pull request 11368. Compare the color-studio dist/color-variables.scss file with Calypso's assets/stylesheets/shared/_colors.scss example, then verify that the stylesheet imports the shared variables instead of defining the colours directly.

Written by the indexing model from the issue text.