Enable clippy::useless_conversion (#8767)

This PR enables the
[`clippy::useless_conversion`](https://rust-lang.github.io/rust-clippy/master/index.html#/useless_conversion)
rule and fixes the outstanding violations.

Release Notes:

- N/A

crates/assistant/src/assistant_panel.rs

@@ -979,7 +979,7 @@ impl AssistantPanel {
             font_size: rems(0.875).into(),
             font_weight: FontWeight::NORMAL,
             font_style: FontStyle::Normal,
-            line_height: relative(1.3).into(),
+            line_height: relative(1.3),
             background_color: None,
             underline: None,
             strikethrough: None,
@@ -1633,7 +1633,6 @@ impl Conversation {
     fn count_remaining_tokens(&mut self, cx: &mut ModelContext<Self>) {
         let messages = self
             .messages(cx)
-            .into_iter()
             .map(|message| tiktoken_rs::ChatCompletionRequestMessage {
                 role: match message.role {
                     Role::User => "user".into(),
@@ -3199,7 +3198,7 @@ impl InlineAssistant {
             font_size: rems(0.875).into(),
             font_weight: FontWeight::NORMAL,
             font_style: FontStyle::Normal,
-            line_height: relative(1.3).into(),
+            line_height: relative(1.3),
             background_color: None,
             underline: None,
             strikethrough: None,