Make background parsing a little more platform agnostic. (#11689)

_Description of what this PR is changing or adding, and why:_

A tiny nit fix to make this topic platform agnostic.

_Issues fixed by this PR (if any):_

_PRs or commits this PR depends on (if any):_

## Presubmit checklist

- [x] This PR is marked as draft with an explanation if not meant to
land until a future stable release.
- [x] This PR doesn’t contain automatically generated corrections
(Grammarly or similar).
- [x] This PR follows the [Google Developer Documentation Style
Guidelines](https://developers.google.com/style) — for example, it
doesn’t use _i.e._ or _e.g._, and it avoids _I_ and _we_ (first person).
- [x] This PR uses [semantic line
breaks](https://github.com/dart-lang/site-shared/blob/main/doc/writing-for-dart-and-flutter-websites.md#semantic-line-breaks)
of 80 characters or fewer.

Author: antfitch

src/content/cookbook/networking/background-parsing.md

@@ -16,9 +16,7 @@ If this work takes more than 16 milliseconds,
 your users experience jank.
 
 To avoid jank, you need to perform expensive computations
-like this in the background.
-On Android, this means scheduling work on a different thread.
-In Flutter, you can use a separate [Isolate][].
+like this in the background, using a separate [Isolate][].
 This recipe uses the following steps:
 
   1. Add the `http` package.