axum-extra: Remove unused tower dependency (#3486)

Author: tottoto

axum-extra/Cargo.toml

@@ -90,7 +90,7 @@ with-rejection = ["dep:axum"]
 
 # Enabled by docs.rs because it uses all-features
 # Enables upstream things linked to in docs
-__private_docs = ["axum/json", "dep:serde"]
+__private_docs = ["axum/json", "dep:serde", "dep:tower"]
 
 [dependencies]
 axum-core = { path = "../axum-core", version = "0.5.2" }
@@ -104,7 +104,6 @@ mime = "0.3"
 pin-project-lite = "0.2"
 rustversion = "1.0.9"
 serde_core = "1.0.221"
-tower = { version = "0.5.2", default-features = false, features = ["util"] }
 tower-layer = "0.3"
 tower-service = "0.3"
 
@@ -129,6 +128,7 @@ typed-json = { version = "0.1.1", optional = true }
 
 # doc dependencies
 serde = { version = "1.0.221", optional = true }
+tower = { version = "0.5.2", default-features = false, features = ["util"], optional = true }
 
 [dev-dependencies]
 axum = { path = "../axum", features = ["macros", "__private"] }