Mark gimli-symbolize feature as deprecated

The backtrace library no longer supports swapping the symbolization
library and always picks gimli (indirectly via addr2line crate). gimli
also has a lot fewer dependencies these days.

Cargo.toml

@@ -18,10 +18,12 @@ keywords = [
 ]
 
 [features]
-default = ["gimli-symbolize"]
-gimli-symbolize = ["backtrace/gimli-symbolize"]
+default = []
 resolve-modules = ["regex"]
 
+# Deprecated, no longer has any effect: backtrace crate removed corresponding option.
+gimli-symbolize = []
+
 [dependencies]
 termcolor = "1.1.2"
 backtrace = "0.3.57"

README.md

@@ -41,21 +41,6 @@ BacktracePrinter::new().message("Custom message!").install(default_output_stream
 - Hide all the frames after the panic was already initiated
 - Hide language runtime initialization frames
 
-### Reducing transitive dependencies
-
-In order to reduce transitive dependencies, you can disable the default
-enabled `gimli-symbolize` feature by adding a `default-features = false`
-clause to your `Cargo.toml` dependency entry, e.g.:
-
-```toml
-[dependencies]
-color-backtrace = { version = "0.6", default-features = false }
-```
-
-This will reduce dependencies from ~50 → ~10. However, you'll pay for it with
-[inaccurate source info](https://github.com/athre0z/color-backtrace/issues/2)
-on macOS and Linux
-
 ### Usage in tests
 
 Unfortunately, defining custom init functions run before tests are started is