Remove `background:` rule from table cells to enable row background-color overrides in wikitext.

Row background falls back to table's background (same), consistent with Vector skin's behaviour.

Bug: T238482
Change-Id: I8bb955265f0ca189d1e6890065a5db510ceac612

resources/screen-common.less

@@ -722,11 +722,6 @@ body :not( :checked ) > .toctogglespan:after {
 	> * > tr > th {
 		border-bottom-width: 2px;
 	}
-
-	> tr > td,
-	> * > tr > td {
-		background: @base90;
-	}
 }
 
 .mw-datatable th {