[REF] mail: move sample_server code in web/ assets

This file override was put in its own folder, requiring to
manually maintain its presence in the mail manifest.

This file is an override of `/web`, therefore it should simply
be moved in the appropriate folder to be automatically taken
into account.

Also took opportunity to add suffix in filename to clarify this
is a patch.

closes odoo#157284

Signed-off-by: Sébastien Theys (seb) <[email protected]>

Author: alexkuhn

addons/mail/__manifest__.py

@@ -129,7 +129,6 @@
             'mail/static/src/**/primary_variables.scss',
         ],
         'web.assets_backend': [
-            'mail/static/src/model/**/*',
             # depends on BS variables, can't be loaded in assets_primary or assets_secondary
             'mail/static/src/scss/variables/derived_variables.scss',
             'mail/static/src/scss/*.scss',