Refactor: Remove ECC_Start and ECC_Stop from key header

They are unused outside of the key module now.

src/key.cpp

@@ -432,7 +432,8 @@ bool ECC_InitSanityCheck() {
     return key.VerifyPubKey(pubkey);
 }
 
-void ECC_Start() {
+/** Initialize the elliptic curve support. May not be called twice without calling ECC_Stop first. */
+static void ECC_Start() {
     assert(secp256k1_context_sign == nullptr);
 
     secp256k1_context *ctx = secp256k1_context_create(SECP256K1_CONTEXT_NONE);
@@ -449,7 +450,8 @@ void ECC_Start() {
     secp256k1_context_sign = ctx;
 }
 
-void ECC_Stop() {
+/** Deinitialize the elliptic curve support. No-op if ECC_Start wasn't called first. */
+static void ECC_Stop() {
     secp256k1_context *ctx = secp256k1_context_sign;
     secp256k1_context_sign = nullptr;
 

src/key.h

@@ -236,12 +236,6 @@ struct CExtKey {
     void SetSeed(Span<const std::byte> seed);
 };
 
-/** Initialize the elliptic curve support. May not be called twice without calling ECC_Stop first. */
-void ECC_Start();
-
-/** Deinitialize the elliptic curve support. No-op if ECC_Start wasn't called first. */
-void ECC_Stop();
-
 /** Check that required EC support is available at runtime. */
 bool ECC_InitSanityCheck();