[Docs] Remove to_list that causes failure in example code

Running the example (`bazel build //MyExample:example --aspects print.bzl%print_aspect`) in the docs threw the following error:

```
Traceback (most recent call last):
	File "/Users/patrickb/.../BUILD", line 3
		//:print.bzl%print_aspect(...)
	File "/Users/patrickb/.../print.bzl", line 6, in _print_aspect_impl
		ctx.rule.attr.srcs.to_list
'list' value has no field or method 'to_list'
```

Removing the `to_list()` fixed it for me since `srcs` is already a `list`.

Closes #11046.

PiperOrigin-RevId: 303963682