Replace the upgradefluxfile builtin with a seperate upgrade-flux-file tool.

This allows us to remove all the SQL stuff from the main program, and restores
the ability to upgrade from version 2 SQL files.

lib/fluxsink/fluxsink.cc

@@ -11,9 +11,6 @@ std::unique_ptr<FluxSink> FluxSink::create(const FluxSinkProto& config)
 {
 	switch (config.dest_case())
 	{
-		case FluxSinkProto::kFluxfile:
-			return createSqliteFluxSink(config.fluxfile());
-
 		case FluxSinkProto::kDrive:
 			return createHardwareFluxSink(config.drive());