i18n: Fix 'add choice' / 'add task' button size.

Removed the CSS rule setting the button's width to 100px.  This lets
the button take as much space as the appropriate translation needs,
without displaying an odd two-line button.

Fixes: #20077

static/styles/widgets.css

@@ -109,7 +109,6 @@ button {
         border-radius: 3px;
         border: 1px solid hsl(0, 0%, 80%);
         background-color: hsl(0, 0%, 100%);
-        width: 100px;
 
         &:hover {
             border-color: hsl(0, 0%, 60%);