input/Plugin: migrate init() from class Error to C++ exceptions

src/input/InputPlugin.hxx

@@ -40,20 +40,6 @@ class Error;
 struct Tag;
 
 struct InputPlugin {
-	enum class InitResult {
-		/**
-		 * A fatal error has occurred (e.g. misconfiguration).
-		 * The #Error has been set.
-		 */
-		ERROR,
-
-		/**
-		 * The plugin was initialized successfully and is
-		 * ready to be used.
-		 */
-		SUCCESS,
-	};
-
 	const char *name;
 
 	/**
@@ -61,8 +47,10 @@ struct InputPlugin {
 	 *
 	 * Throws #PluginUnavailable if the plugin is not available
 	 * and shall be disabled.
+	 *
+	 * Throws std::runtime_error on (fatal) error.
 	 */
-	InitResult (*init)(const ConfigBlock &block, Error &error);
+	void (*init)(const ConfigBlock &block);
 
 	/**
 	 * Global deinitialization.  Called once before MPD shuts