config_proc_macro: reduce syn's features

Author: klensy

config_proc_macro/Cargo.toml

@@ -13,7 +13,7 @@ proc-macro = true
 [dependencies]
 proc-macro2 = "1.0"
 quote = "1.0"
-syn = { version = "2.0", features = ["full", "visit"] }
+syn = { version = "2.0", default-features = false, features = ["full", "parsing", "proc-macro", "printing"] }
 
 [dev-dependencies]
 serde = { version = "1.0.160", features = ["derive"] }