Don't unwrap CLJC lib specs when cleaning a namespace

We have a namespace like this:

```cljc
(ns my.app.ns
(:require [vlad.core :as vlad :refer [attr chain join present Validation]]
#? (:cljs [goog.date.Interval :as Interval])
[clojure.string :as string]
[cemerick.url :as url]))
```

after running `cljr-clean-ns`, it fully expands the clj and cljs versions to:

```cljc
(ns my.app.ns
#?@
(:clj
[(:require
[cemerick.url :as url]
[clojure.string :as string]
[vlad.core :as vlad :refer [attr chain join present Validation]])]
:cljs
[(:require
[cemerick.url :as url]
[clojure.string :as string]
[goog.date.Interval :as Interval]
[vlad.core :as vlad :refer [attr chain join present Validation]])]))
```

This namespace form is twice as long, and (IMO) obscures which parts of the namespace differ between clj and cljs. To tell the difference, you need to check each line and find the corresponding one in the other branch.

Would you consider a feature request to not fully expand CLJC forms in the `:require`?

I'd argue this should be the default behaviour, but could also see it being an option if people liked this kind of expansion. The new feature wouldn't automatically convert fully expanded CLJC forms back, it would just preserve what was already there.