Remove striped tables in UI (#36509)

We've been cutting down on the "striped" tables (where rows are using
alternate row background colors). This completely removes them as I
think such a design looks outdated.

The removal of selectors starting with `.ui[class*="very
basic"].table:not(.striped)` is needed because of a specificity issue in
the CSS where table cells would otherwise render with incorrect padding.

Example of one affected table:

<img width="1027" height="224" alt="image"
src="https://github.com/user-attachments/assets/2f3006ca-99a1-4655-afdb-b7cd9e5f19c7"
/>

web_src/css/repo.css

@@ -774,10 +774,6 @@ td .commit-summary {
   width: 200px;
 }
 
-.repository #commits-table.ui.basic.striped.table tbody tr:nth-child(2n) {
-  background-color: var(--color-light) !important;
-}
-
 .repository .data-table {
   width: 100%;
 }