search: remove quote hint in regex mode if pattern contains colon

Created by: rvantonder

In favor of removing this. It's related to improving other quoting hints, which I'll get to later (https://github.com/sourcegraph/sourcegraph/issues/12802, https://github.com/sourcegraph/sourcegraph/issues/10793, https://github.com/sourcegraph/sourcegraph/issues/11909).

As in: I half-know what I’m doing here by using regex. I appreciate the hint though, when I use it the first time.

I don't think there's any way to make this dismissible. The usefulness showing this on first time is outweighed by this showing up every time, and regex is an opt-in toggle, so we can mostly safely assume the user knows what they're dealing with.

Context: