Fix various performance issues reported by cppcheck (#5628)

* Also remove 1 non declared but defined functions

src/guiEngine.h

@@ -80,7 +80,7 @@ public:
 	 * receive text/events transmitted by guiFormSpecMenu
 	 * @param text textual representation of event
 	 */
-	void gotText(std::wstring text);
+	void gotText(const std::wstring &text);
 
 private:
 	/** target to transmit data to */
@@ -260,14 +260,11 @@ private:
 	 * @param url url to download
 	 * @param target file to store to
 	 */
-	static bool downloadFile(std::string url,std::string target);
+	static bool downloadFile(const std::string &url, const std::string &target);
 
 	/** array containing pointers to current specified texture layers */
 	image_definition m_textures[TEX_LAYER_MAX];
 
-	/** draw version string in topleft corner */
-	void drawVersion();
-
 	/**
 	 * specify text to appear as top left string
 	 * @param text to set