Merge rust-bitcoin#4971: Do not enable secp rand feature

bd3c5f5 Do not enable secp rand feature (Tobin C. Harding)

Pull request description:

  Patch f80cf2c (PR rust-bitcoin#4154) somehow got past review with a change that unconditionally enabled `rand` feature for `secp256k1` - this is incorrect.
  
  There is no mention of the change in the PR description or review comments - review fail.


ACKs for top commit:
  apoelstra:
    ACK bd3c5f5; successfully ran local tests


Tree-SHA512: 832228b8b484d2ad3f6b7bf29fcd5885702730ef430d7e39efa01b8b68e1e13ea10b3ac8e42d16cc3588e36a8dc34e4d8a3a77aec5d998ded4378e8f1aebd66b

Author: apoelstra

bitcoin/Cargo.toml

@@ -33,7 +33,7 @@ hex = { package = "hex-conservative", version = "0.3.0", default-features = fals
 internals = { package = "bitcoin-internals", path = "../internals", features = ["alloc", "hex"] }
 io = { package = "bitcoin-io", path = "../io", default-features = false, features = ["alloc", "hashes"] }
 primitives = { package = "bitcoin-primitives", path = "../primitives", default-features = false, features = ["alloc", "hex"] }
-secp256k1 = { version = "0.30.0", default-features = false, features = ["hashes", "alloc", "rand"] }
+secp256k1 = { version = "0.30.0", default-features = false, features = ["hashes", "alloc"] }
 units = { package = "bitcoin-units", path = "../units", default-features = false, features = ["alloc"] }
 
 arbitrary = { version = "1.4.1", optional = true }