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/init.cpp

@@ -32,6 +32,8 @@
 #include <interfaces/chain.h>
 #include <interfaces/init.h>
 #include <interfaces/node.h>
+#include <kernel/context.h>
+#include <key.h>
 #include <logging.h>
 #include <mapport.h>
 #include <net.h>
@@ -75,6 +77,7 @@
 #include <util/fs_helpers.h>
 #include <util/moneystr.h>
 #include <util/result.h>
+#include <util/signalinterrupt.h>
 #include <util/strencodings.h>
 #include <util/string.h>
 #include <util/syserror.h>
@@ -371,6 +374,7 @@ void Shutdown(NodeContext& node)
     node.chainman.reset();
     node.validation_signals.reset();
     node.scheduler.reset();
+    node.ecc_context.reset();
     node.kernel.reset();
 
     RemovePidFile(*node.args);
@@ -1084,6 +1088,10 @@ bool AppInitSanityChecks(const kernel::Context& kernel)
         return InitError(strprintf(_("Initialization sanity check failed. %s is shutting down."), PACKAGE_NAME));
     }
 
+    if (!ECC_InitSanityCheck()) {
+        return InitError(strprintf(_("Elliptic curve cryptography sanity check failure. %s is shutting down."), PACKAGE_NAME));
+    }
+
     // Probe the data directory lock to give an early error message, if possible
     // We cannot hold the data directory lock here, as the forking for daemon() hasn't yet happened,
     // and a fork will cause weird behavior to it.