docs: remove invalid path = line from MarkdownContent sample

docs: fix MarkdownContent sample by removing invalid `path =` line

The sample currently contains a dangling `path =` statement that causes
compilation errors. This property does not exist on ContentPage, and the
example already uses `doc_path` correctly in OpenUrlCommand.

Author: BitRyuu

hub/powertoys/command-palette/using-markdown-content.md

@@ -100,7 +100,6 @@ public class <ExtensionName>Page : ContentPage
         Icon = new("\uE8A5"); // Document icon
         Title = "Markdown page";
         Name = "Preview file";
-        path = 
 
 +       Commands = [
 +           new CommandContextItem(new OpenUrlCommand(doc_path)) { Title = "Open in File Explorer" },