Make popup titles left-aligned

In some cases when expanding popups with centered titles horizontally,
the title would jump right and left by one character. The new popups
also look more like the lazygit popups.

src/ui/widgets/popup.rs

@@ -64,8 +64,7 @@ impl Popup {
                         .style(self.border_style),
                 )
                 .horizontal(2),
-            )
-            .horizontal(0.5);
+            );
             Layer::new(vec![window.into(), title.into()]).into()
         } else {
             window.into()