Remove references to deleted about-*.js files

Auditors: @bbondy

Author: diracdeltas

app/extensions/brave/about-downloads.html

@@ -10,7 +10,6 @@
     <meta name='theme-color' content='#000080'>
     <link rel="shortcut icon"type="image/x-icon" href="data:image/x-icon;,">
     <title data-l10n-id="downloads"></title>
-    <script src='js/about-downloads.js'></script>
     <script src='js/about.js'></script>
     <script src="ext/l20n.min.js" async></script>
     <link rel="localization" href="locales/{locale}/downloads.properties">

app/extensions/brave/about-flash.html

@@ -9,7 +9,6 @@
     <meta name="defaultLanguage" content="en-US">
     <meta name='theme-color' content='#ff5000'>
     <title data-l10n-id="flashTitle"></title>
-    <script src='js/about-flash.js'></script>
     <script src='js/about.js'></script>
     <script src="ext/l20n.min.js" async></script>
     <link rel="localization" href="locales/{locale}/app.properties">

app/extensions/brave/about-passwords.html

@@ -9,7 +9,6 @@
     <meta name="defaultLanguage" content="en-US">
     <meta name='theme-color' content='#ff5000'>
     <title data-l10n-id="passwordsTitle"></title>
-    <script src='js/about-passwords.js'></script>
     <script src='js/about.js'></script>
     <script src="ext/l20n.min.js" async></script>
     <link rel="localization" href="locales/{locale}/passwords.properties">

app/extensions/brave/about-preferences.html

@@ -10,7 +10,6 @@
     <meta name='theme-color' content='#ff5000'>
     <link rel="shortcut icon"type="image/x-icon" href="data:image/x-icon;,">
     <title data-l10n-id="preferences"></title>
-    <script src='js/about-preferences.js'></script>
     <script src='js/about.js'></script>
     <script src="ext/l20n.min.js" async></script>
     <link rel="localization" href="locales/{locale}/preferences.properties">