kernel: remove btck_chain_get_genesis

It is equivalent to calling btck_chain_get_by_height(0).

src/kernel/bitcoinkernel.cpp

@@ -1242,12 +1242,6 @@ int btck_chain_get_height(const btck_Chain* chain)
     return btck_Chain::get(chain).Height();
 }
 
-const btck_BlockTreeEntry* btck_chain_get_genesis(const btck_Chain* chain)
-{
-    LOCK(::cs_main);
-    return btck_BlockTreeEntry::ref(btck_Chain::get(chain).Genesis());
-}
-
 const btck_BlockTreeEntry* btck_chain_get_by_height(const btck_Chain* chain, int height)
 {
     LOCK(::cs_main);

src/kernel/bitcoinkernel.h

@@ -1222,15 +1222,6 @@ BITCOINKERNEL_API const btck_BlockTreeEntry* BITCOINKERNEL_WARN_UNUSED_RESULT bt
 BITCOINKERNEL_API int32_t BITCOINKERNEL_WARN_UNUSED_RESULT btck_chain_get_height(
     const btck_Chain* chain) BITCOINKERNEL_ARG_NONNULL(1);
 
-/**
- * @brief Get the block tree entry of the genesis block.
- *
- * @param[in] chain Non-null.
- * @return          The block tree entry of the genesis block, or null if the chain is empty.
- */
-BITCOINKERNEL_API const btck_BlockTreeEntry* BITCOINKERNEL_WARN_UNUSED_RESULT btck_chain_get_genesis(
-    const btck_Chain* chain) BITCOINKERNEL_ARG_NONNULL(1);
-
 /**
  * @brief Retrieve a block tree entry by its height in the currently active chain.
  * Once retrieved there is no guarantee that it remains in the active chain.

src/kernel/bitcoinkernel_wrapper.h

@@ -982,11 +982,6 @@ public:
         return btck_chain_get_height(get()) + 1;
     }
 
-    BlockTreeEntry Genesis() const
-    {
-        return btck_chain_get_genesis(get());
-    }
-
     BlockTreeEntry GetByHeight(int height) const
     {
         auto index{btck_chain_get_by_height(get(), height)};

src/test/kernel/test_kernel.cpp

@@ -664,7 +664,7 @@ void chainman_reindex_test(TestDirectory& test_directory)
     // Sanity check some block retrievals
     auto chain{chainman->GetChain()};
     BOOST_CHECK_THROW(chain.GetByHeight(1000), std::runtime_error);
-    auto genesis_index{chain.Genesis()};
+    auto genesis_index{chain.Entries().front()};
     BOOST_CHECK(!genesis_index.GetPrevious());
     auto genesis_block_raw{chainman->ReadBlock(genesis_index).value().ToBytes()};
     auto first_index{chain.GetByHeight(0)};