[FIX] web_editor: remove the use of website color in backend

Since [this commit], the color of the links in the backend is set to the
value of the variable `o-cc3-link`. This causes problems... Firstly,
this variable is defined in the website module, but it is used in the
web_editor module, which does not depend of website. Secondly, this
variable declared in website is made to be modified by the website
administrator via the edit panel (the theme tab). This commit corrects
this by replacing the use of this variable with a hardcoded color.

Steps to reproduce the bug fixed by this commit:
- Have website and project installed
- In the description of a project task, create a link
- Edit a website page
- Go to the theme tab
- Click on Colors Preset
- Open the 3rd preset
- Change the color for "Links" (to red for example)

=> Go back to the project task where you put a link. The link is now red
(this may require a page refresh). But the website option should not
change the links in the backend.

This commit removes the website builder related color o-cc-3-link
usage for editor links.

[this commit]: https://github.com/odoo/odoo/commit/5d598e4269431222ae28ac2196ff6f1f45466734

task-3275134

closes odoo/odoo#142542

X-original-commit: 6f10705e043115369ec581a83f65482ea83d25c8
Signed-off-by: Romain Derie (rde) <rde@odoo.com>
Signed-off-by: Guillaume Dieleman (gdi) <gdi@odoo.com>

addons/web_editor/static/src/scss/web_editor.backend.scss

@@ -43,10 +43,7 @@
     }
     a:not(.btn) {
         // Ensure non-button links are visible enough in the editor.
-        $oe-link-color: o-color('o-cc3-link');
-        @if ($oe-link-color) {
-            color: $oe-link-color;
-        }
+        color: #008f8c;
     }
 }