Reduce transitive dependencies in the image crate

Neovide only needs to read .ico images so we can remove all other
formats. This brings the number of dependencies from 391 to 368 on
Linux.

Cargo.toml

@@ -24,7 +24,7 @@ lru = "0.4.3"
 derive-new = "0.5"
 rmpv = "0.4.4"
 rust-embed = { version = "5.2.0", features = ["debug-embed"] }
-image = "0.22.3"
+image = { version = "0.22.3", default-features = false, features = ["ico"] }
 nvim-rs = { git = "https://github.com/KillTheMule/nvim-rs", branch = "master", features = ["use_tokio"] }
 tokio = { version = "1.1.1", features = ["full"] }
 tokio-util = "0.6.7"