cargo: Update and cleanup dependencies

- Replace one remaining use of util::spawn with gio
- Replace pretty_env_logger with env_logger

Part-of: <https://gitlab.gnome.org/Incubator/loupe/-/merge_requests/149>

Cargo.toml

@@ -12,19 +12,15 @@ codegen-units = 1
 [dependencies]
 anyhow = { version = "1.0.66", features = ["backtrace"] }
 arc-swap = "1.6.0"
-async-global-executor = "2.3.1"
-async-std = "1.12.0"
+env_logger = "0.10.0"
 futures = "0.3.25"
-futures-channel = "0.3.25"
 gtk-macros = "0.3.0"
 indexmap = "1.9.2"
 kamadak-exif = "0.5.5"
 libgweather = "4.2.0"
 log = "0.4.17"
 once_cell = "1.16.0"
-pretty_env_logger = "0.4.0"
 safe-transmute = "0.11.2"
-url = "2.3.1"
 
 # decoders
 image-rs = { package = "image", version = "*", git = "https://github.com/image-rs/image.git" }