Remove broken assert

See #12326

I have been able to trigger this pretty reliably, and the simplest fix is
to... just not assert out when we would return anyway.

It doesn't reproduce with `commandline` because it needs the
suggestion to exist, it'll happen when you enter the "n" of "install"
if the suggestion is "İnstall" (i.e. uppercase turkish dotted i)

In general asserts in the reader make for a terrible experience.

src/reader/reader.rs

@@ -5495,11 +5495,6 @@ fn update_autosuggestion(&mut self) {
         let el = &self.data.command_line;
         let autosuggestion = &self.autosuggestion;
         if self.is_at_line_with_autosuggestion() {
-            assert!(string_prefixes_string_maybe_case_insensitive(
-                autosuggestion.icase,
-                &el.text()[autosuggestion.search_string_range.clone()],
-                &autosuggestion.text
-            ));
             return;
         }