[FIX] web: domain selector background color

This commit, remove the not mandatory CSS rule on the input for the
`Domain Selector` modal, and so the input uses the transparent color.

Steps to reproduce:
* Open Odoo (Enterprise)
* Activate the dark mode
* Open a App (e.g.: Contact)
* Add a filter in the search bar
* Click on the filter icon in the facet
  => The background inputs are white with white text color => BUG

closes odoo/odoo#129842

X-original-commit: d36505edec607161c6884892e8de34d42a10f207
Signed-off-by: Adrien Dieudonné (adr) <adr@odoo.com>
Signed-off-by: Romeo Fragomeli (rfr) <rfr@odoo.com>

addons/web/static/src/core/domain_selector/domain_selector.scss

@@ -122,7 +122,6 @@
 
                 > * {
                     width: auto;
-                    background-color: white;
 
                     &.o_model_field_selector {
                         flex: 0 1 40%;