Avoid 'rawrow' for HTMLForm 'info' fields

The wrapper tags that we have to create when using the 'rawrow' option
would have to be different for OOUI and non-OOUI preferences forms,
making it impossible to support both at the same time.

We used it in order to generate `<td colspan=2>...</td>` rather than
`<td></td><td>...</td>`, and make the description span both the label
and the input columns. However, this is not necessary, because the
label column is entirely hidden on this page of preferences, as all of
the preferences have no labels.

Bug: T203202
Change-Id: Ib9510a8bfb2430fdda3988d88628c9f0c509c6d0

includes/GadgetHooks.php

@@ -114,12 +114,9 @@ class GadgetHooks {
 		$preferences['gadgets-intro'] =
 			[
 				'type' => 'info',
-				'default' => Xml::tags( 'tr', [],
+				'default' => wfMessage( 'gadgets-prefstext' )->parseAsBlock(),
-					Xml::tags( 'td', [ 'colspan' => 2 ],
-						wfMessage( 'gadgets-prefstext' )->parseAsBlock() ) ),
 				'section' => 'gadgets',
-				'rawrow' => true,
+				'raw' => true,
-				'raw' => true, // Needed to pass phan-taint-check-plugin, see T201902
 			];
 
 		$preferences['gadgets'] =