Ignore text properties in straight--process-get-output (#588)
Ignore text properties in straight--process-get-output (#588)

`straight--process-get-output` uses `buffer-substring` to copy the
output of a process, which means that the text properties are copied
too. Most of the time, this is fine, as there are no text properties.

However, when using the [`ws-butler`] package, the `ws-butler-chg`
text property is present and copied. This means that, for example,
`straight-freeze-versions` produces a `default.el` file looking like
this:

```emacs-lisp
(("alert" . #("7046393272686c7a1a9b3e7f7b1d825d2e5250a6" 0 40 (ws-butler-chg chg)))
 ("anchored-transpose" . #("43b37bbc5dc0fe4b7b1b46c5e1d98553e9b527ae" 0 40 (ws-butler-chg chg)))
 ..)
```

while it should be:

```emacs-lisp
(("alert" . "7046393272686c7a1a9b3e7f7b1d825d2e5250a6")
 ("anchored-transpose" . "43b37bbc5dc0fe4b7b1b46c5e1d98553e9b527ae")
 ..)
```

Fix this by using `buffer-substring-no-properties` instead of
`buffer-substring`.

[`ws-butler`]: https://github.com/lewang/ws-butler
raxod502/straight.el,raxod502/straight.el