deps: remove unused feature `subxt/substrate-compat` (#7643)

Partly fixes #7403

Subxt depends still on sp-crypto-hashing v0.7 but it's only one
dependency after removing the substrate-compat feature which is probably
"acceptable"

polkadot/zombienet-sdk-tests/Cargo.toml

@@ -15,7 +15,7 @@ log = { workspace = true }
 polkadot-primitives = { workspace = true, default-features = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
-subxt = { workspace = true, features = ["substrate-compat"] }
+subxt = { workspace = true }
 subxt-signer = { workspace = true }
 tokio = { workspace = true, features = ["rt-multi-thread"] }
 tokio-util = { workspace = true, features = ["time"] }