kernel: Remove key module from kernel library

The key module's functionality is not used by the kernel library, but
currently kernel users are still required to initialize the key module's
`secp256k1_context_sign` global as part of the `kernel::Context` through
`ECC_Start`.

src/node/context.cpp

@@ -8,6 +8,7 @@
 #include <banman.h>
 #include <interfaces/chain.h>
 #include <kernel/context.h>
+#include <key.h>
 #include <net.h>
 #include <net_processing.h>
 #include <netgroup.h>
@@ -16,6 +17,7 @@
 #include <scheduler.h>
 #include <txmempool.h>
 #include <validation.h>
+#include <validationinterface.h>
 
 namespace node {
 NodeContext::NodeContext() = default;

src/node/context.h

@@ -5,10 +5,7 @@
 #ifndef BITCOIN_NODE_CONTEXT_H
 #define BITCOIN_NODE_CONTEXT_H
 
-#include <kernel/context.h>
-
 #include <atomic>
-#include <cassert>
 #include <cstdlib>
 #include <functional>
 #include <memory>
@@ -24,6 +21,7 @@ class ValidationSignals;
 class CScheduler;
 class CTxMemPool;
 class ChainstateManager;
+class ECC_Context;
 class NetGroupManager;
 class PeerManager;
 namespace interfaces {
@@ -32,6 +30,12 @@ class ChainClient;
 class Init;
 class WalletLoader;
 } // namespace interfaces
+namespace kernel {
+struct Context;
+}
+namespace util {
+class SignalInterrupt;
+}
 
 namespace node {
 class KernelNotifications;
@@ -49,6 +53,7 @@ class KernelNotifications;
 struct NodeContext {
     //! libbitcoin_kernel context
     std::unique_ptr<kernel::Context> kernel;
+    std::unique_ptr<ECC_Context> ecc_context;
     //! Init interface for initializing current process and connecting to other processes.
     interfaces::Init* init{nullptr};
     //! Interrupt object used to track whether node shutdown was requested.

src/node/interfaces.cpp

@@ -17,6 +17,7 @@
 #include <interfaces/node.h>
 #include <interfaces/wallet.h>
 #include <kernel/chain.h>
+#include <kernel/context.h>
 #include <kernel/mempool_entry.h>
 #include <logging.h>
 #include <mapport.h>
@@ -99,6 +100,7 @@ public:
         if (!AppInitParameterInteraction(args())) return false;
 
         m_context->kernel = std::make_unique<kernel::Context>();
+        m_context->ecc_context = std::make_unique<ECC_Context>();
         if (!AppInitSanityChecks(*m_context->kernel)) return false;
 
         if (!AppInitLockDataDirectory()) return false;

src/node/kernel_notifications.cpp

@@ -14,6 +14,7 @@
 #include <node/abort.h>
 #include <node/interface_ui.h>
 #include <util/check.h>
+#include <util/signalinterrupt.h>
 #include <util/strencodings.h>
 #include <util/string.h>
 #include <util/translation.h>