Remove intro02.py

It doesn't appear to be referenced anywhere in the docs.

docs/examples/tutorial/intro02.py

@@ -1,29 +0,0 @@
-from textual.app import App
-
-
-class ExampleApp(App):
-
-    COLORS = [
-        "white",
-        "maroon",
-        "red",
-        "purple",
-        "fuchsia",
-        "olive",
-        "yellow",
-        "navy",
-        "teal",
-        "aqua",
-    ]
-
-    def on_mount(self):
-        self.styles.background = "darkblue"
-
-    def on_key(self, event):
-        if event.key.isdigit():
-            self.styles.background = self.COLORS[int(event.key)]
-        self.bell()
-
-
-app = ExampleApp()
-app.run()