Improve streaming git diffs to be less jumpy during inline assistant generation (#15853)

Release Notes:

- Improved streaming git diffs to be less jumpy during inline assistant
generation

---------

Co-authored-by: Antonio Scandurra <antonio@zed.dev>

crates/assistant/Cargo.toml

@@ -65,7 +65,6 @@ semantic_index.workspace = true
 serde.workspace = true
 serde_json.workspace = true
 settings.workspace = true
-similar.workspace = true
 smol.workspace = true
 telemetry_events.workspace = true
 terminal.workspace = true