Remove deprecated _ec_privkey_{negate,tweak_add,tweak_mul} aliases

These function aliases have been described as DEPRECATED in the public
API docs already many years ago (see #701, commit 41fc7856), and in
addition explicit deprecation warnings are shown by the compiler at
least since the first official release 0.2.0 (see PR #1089, commit
fc94a2da), so it should be fine to just remove them by now.

Co-authored-by: Tim Ruffing <crypto@timruffing.de>

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+#### Removed
+- Removed previously deprecated function aliases `secp256k1_ec_privkey_negate`, `secp256k1_ec_privkey_tweak_add` and
+  `secp256k1_ec_privkey_tweak_mul`. Use `secp256k1_ec_seckey_negate`, `secp256k1_ec_seckey_tweak_add` and
+  `secp256k1_ec_seckey_tweak_mul` instead.
+
 ## [0.6.0] - 2024-11-04
 
 #### Added