Fix phases table styles on small screens

The "enabled" column was aligned to the center, which looked weird when
seen on small screens because the `table-for-mobile` class (which I
think was added by accident) shows `th` and `td` elements using
`display: block`. Besides, using `display: block` on these elements
means browsers don't identify them as table headings/cells anymore,
causing accessibility issues.

app/components/admin/budget_phases/phases_component.html.erb

@@ -1,5 +1,5 @@
 <% if phases.present? %>
-  <table class="budget-phases-table table-for-mobile">
+  <table class="budget-phases-table">
     <caption><%= t("admin.budgets.edit.phases_caption") %></caption>
     <thead>
       <tr>