[Intl] Remove warning about replacement layer

The "replacement layer" mentionned in the first block on the page has been deprecated in 5.3 (and removed in 6.0).

(that's why i target 6.3+ and not 5.4 -- where it still makes sense to mention it)


```
.. caution::

    The replacement layer is limited to the ``en`` locale. If you want to use
    other locales, you should `install the intl extension`_. There is no conflict
    between the two because, even if you use the extension, this package can still
    be useful to access the ICU data.
```

Author: smnandre

components/intl.rst

@@ -3,13 +3,6 @@ The Intl Component
 
     This component provides access to the localization data of the `ICU library`_.
 
-.. caution::
-
-    The replacement layer is limited to the ``en`` locale. If you want to use
-    other locales, you should `install the intl extension`_. There is no conflict
-    between the two because, even if you use the extension, this package can still
-    be useful to access the ICU data.
-
 .. seealso::
 
     This article explains how to use the Intl features as an independent component