Switch icon (#16363)

Updates instances of the `MagicWand` icon to our more recent `Sparkle` /
`ZedAssistant` icon in places where we reference inline assist.

Before:

![CleanShot 2024-08-16 at 13 41
58@2x](https://github.com/user-attachments/assets/67af27a2-a09b-44bb-a8af-2bafcbbd9038)

After:
![CleanShot 2024-08-16 at 13 48
34@2x](https://github.com/user-attachments/assets/229ccc8e-8a93-44c1-abe0-7b6e22ca93e2)


Release Notes:

- Updated inline assist icon in the editor & terminal.

crates/ui/src/components/icon.rs

@@ -195,7 +195,6 @@ pub enum IconName {
     LineHeight,
     Link,
     ListTree,
-    MagicWand,
     MagnifyingGlass,
     MailOpen,
     Maximize,
@@ -359,7 +358,6 @@ impl IconName {
             IconName::LineHeight => "icons/line_height.svg",
             IconName::Link => "icons/link.svg",
             IconName::ListTree => "icons/list_tree.svg",
-            IconName::MagicWand => "icons/magic_wand.svg",
             IconName::MagnifyingGlass => "icons/magnifying_glass.svg",
             IconName::MailOpen => "icons/mail_open.svg",
             IconName::Maximize => "icons/maximize.svg",