[refactor] Drop form-id template property

In preparation for using the SkinMustache class and
core buildSearchProps method [1],
and to reduce the risk of that change,
move the ID from the template
data to the template itself:

[1] https://github.com/wikimedia/mediawiki/blob/master/includes/skins/SkinMustache.php#L93

Change-Id: I8d62ea6b1adf6ef0cbfa20e1876806eba70b169f

includes/VectorTemplate.php

@@ -498,7 +498,6 @@ class VectorTemplate extends BaseTemplate {
 		$config = $this->getConfig();
 		$props = [
 			'form-action' => $config->get( 'Script' ),
-			'form-id' => 'simpleSearch',
 			'html-button-search-fallback' => $this->makeSearchButton(
 				'fulltext',
 				[ 'id' => 'mw-searchButton', 'class' => 'searchButton mw-fallbackSearchButton' ]

includes/templates/SearchBox.mustache

@@ -6,7 +6,7 @@
 		<label for="searchInput">{{msg-search}}</label>
 	</h3>
 	<form action="{{form-action}}" id="searchform">
-		<div id="{{form-id}}">
+		<div id="simpleSearch">
 			{{{html-input}}}
 			<input type="hidden" name="title" value="{{page-title}}">
 			{{!	We construct two buttons (for 'go' and 'fulltext' search modes), but only one will be

stories/SearchBox.stories.data.js

@@ -10,7 +10,6 @@ export const searchBoxData = {
 	'form-action': '/w/index.php',
 	'html-userlangattributes': htmluserlangattributes,
 	'msg-search': 'Search',
-	'form-id': 'simpleSearch',
 	'html-input': '<input type="search" name="search" placeholder="Search Wikipedia" title="Search Wikipedia [⌃⌥f]" accesskey="f" id="searchInput" autocomplete="off">',
 	'page-title': 'Special:Search',
 	'html-button-search-fallback': '<input type="submit" name="fulltext" value="Search" title="Search pages for this text" id="mw-searchButton" class="searchButton mw-fallbackSearchButton"/>',

stories/types.js

@@ -42,7 +42,6 @@
  * @prop {string|null} msg-search
  * @prop {string} [html-userlangattributes]
  * @prop {string} form-action URL
- * @prop {string} form-id
  * @prop {string|null} html-input
  * @prop {string|null} page-title the title of the search page
  * @prop {string|null} html-button-search-fallback