Disable Serde's default-features

With this patch, 'use-serde' will no longer compile serde/std. Serde/std
has been reexported as 'serde-std', for those who wish to continue to
use it.

Cargo.toml

@@ -18,6 +18,7 @@ base64 = [ "base64-compat" ]
 unstable = []
 rand = ["secp256k1/rand-std"]
 use-serde = ["serde", "bitcoin_hashes/serde", "secp256k1/serde"]
+serde-std = ["serde/std"]
 secp-lowmemory = ["secp256k1/lowmemory"]
 secp-recovery = ["secp256k1/recovery"]
 
@@ -41,7 +42,7 @@ core2 = { version = "0.3.0", optional = true, default-features = false }
 
 base64-compat = { version = "1.0.0", optional = true }
 bitcoinconsensus = { version = "0.19.0-3", optional = true }
-serde = { version = "1", features = [ "derive" ], optional = true }
+serde = { version = "1", default-features = false, features = [ "derive" ], optional = true }
 hashbrown = { version = "0.8", optional = true }
 
 [dev-dependencies]

contrib/test.sh

@@ -93,7 +93,7 @@ if [ "$AS_DEPENDENCY" = true ]
 then
     cargo new dep_test
     cd dep_test
-    echo 'bitcoin = { path = "..", features = ["use-serde"] }' >> Cargo.toml
+    echo 'bitcoin = { path = "..", features = ["use-serde", "serde-std"] }' >> Cargo.toml
 
     # Pin `cc` for Rust 1.29
     if [ -n "$PIN_VERSIONS" ]; then