Remove outdated rule on single quotes in docs (reduxjs#3495)

* Remove outdated rule on single quotes in docs

In PR reduxjs#1874, a mass replacement of angled single quotes ’ with ASCII
single quotes ' was approved. Since then, the docs have contained a
mixture of angled and ASCII single quotes:

```
$ git log -S’ --since="Mon Aug 1 16:45:58 2016 -0400" --pretty=oneline |
wc -l
17
```

so it does not make sense to state a rule on them.

* Remove typographic stuff we don't use anyways.


Former-commit-id: 99bbd43
Former-commit-id: 4d3298d

CONTRIBUTING.md.REMOVED.git-id

@@ -1 +1 @@
-16b40f644637ce759249d1f424bbebcc457fcc68
+73c8c1d715e55d75c4c0f2c0b7f31a2fd8600e2b