gui/game_version: Fix Open Log File button being missing

In commit fc7c87b765 someone missed the
logic surrounding the Open Log File button's setup that should've been
made not Windows-specific anymore.

This commit enables the Open Log File button back whenever Wesnoth has
a log file open for the current session. It also removes a few more
leftovers of the old Windows-specific UI layout path.

data/gui/window/game_version.cfg

@@ -151,27 +151,14 @@
 		[column]
 			horizontal_alignment = right
 			vertical_alignment = top
+			border = all
+			border_size = 5
 
-			[grid]
-				id = "win32_paths"
-
-				[row]
-
-					[column]
-						border = all
-						border_size = 5
-
-						[button]
-							id = "open_stderr"
-							label = _ "Open Log File"
-							tooltip = _ "Opens the log file, which may contain useful debug information"
-						[/button]
-					[/column]
-
-				[/row]
-
-			[/grid]
-
+			[button]
+				id = "open_stderr"
+				label = _ "Open Log File"
+				tooltip = _ "Opens the log file, which may contain useful debug information"
+			[/button]
 		[/column]
 
 	[/row]

src/gui/dialogs/game_version_dialog.cpp

@@ -142,15 +142,9 @@ void game_version::pre_show(window& window)
 		}
 	}
 
-#ifndef _WIN32
-	for(const auto& wid : {"win32_paths"}) {
-		find_widget<widget>(&window, wid, false).set_visible(widget::visibility::invisible);
-	}
-#else
 	button& stderr_button = find_widget<button>(&window, "open_stderr", false);
 	connect_signal_mouse_left_click(stderr_button, std::bind(&game_version::browse_directory_callback, this, log_path_));
 	stderr_button.set_active(!log_path_.empty());
-#endif
 
 	//
 	// Build info tab.