fix: use only one 180x180px touch icon (#1213)

* Include just one 180x180px touch icon`.

  Over time as Apple released different size displays for their
  devices, the requirements¹ for the size of the touch icon have
  changed quite a bit:

   * 57×57px – iPhone with @1x display and iPod Touch
   * 72×72px – iPad and iPad mini with @1x display running iOS ≤ 6
   * 76×76px – iPad and iPad mini with @1x display running iOS ≥ 7
   * 114×114px – iPhone with @2x display running iOS ≤ 6
   * 120×120px – iPhone with @2x and @3x display running iOS ≥ 7
   * 144×144px – iPad and iPad mini with @2x display running iOS ≤ 6
   * 152×152px – iPad and iPad mini with @2x display running iOS 7
   * 180×180px – iPad and iPad mini with @2x display running iOS 8+

  However, most iOS users will be on the latest 2 versions² of iOS
  and using newer devices, so nowadays, one 180x180px touch icon is
  enough.

  Also, if needed, the icon will be automatically³ downscaled by
  Safari, and the result of the scaling is generally ok.

* Remove unneeded `sizes` attribute.

  When using only one touch icon there is no need to use the `sizes`
  attribute.

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¹ h5bp/html5-boilerplate#1599 (comment)
² https://developer.apple.com/support/app-store/
³ https://realfavicongenerator.net/blog/how-ios-scales-the-apple-touch-icon/

See also: https://mathiasbynens.be/notes/touch-icons

src/build/template.html

@@ -10,8 +10,7 @@
 
   <link id='theManifest' rel='manifest' href='/manifest.json' >
   <link id='theFavicon' rel='icon' type='image/png' href='/favicon.png' >
-  <link rel="apple-touch-icon" sizes="120x120" href="/apple-icon-120.png" >
-  <link rel="apple-touch-icon" sizes="180x180" href="/apple-icon-180.png" >
+  <link rel="apple-touch-icon" href="/apple-icon.png" >
   <meta name="mobile-web-app-capable" content="yes" >
   <meta name="apple-mobile-web-app-title" content="Pinafore" >
   <meta name="apple-mobile-web-app-status-bar-style" content="white" >