refactor(docs-infra): remove the Windows tile icons and other unused icons

The `msapplication` tile configuration serves no purpose now, so the
`browserconfig.xml` it points at, the five tile images and the two meta tags
in `index.html` are removed together.

`shared-docs/icons/twitter.svg` is also unused, left behind when the footer
moved to X and Bluesky. Its three siblings in that directory are all still
referenced.

adev/shared-docs/icons/twitter.svg

@@ -1,3 +0,0 @@
-<svg width="17" height="16" viewBox="0 0 17 16" fill="none" xmlns="http://www.w3.org/2000/svg">
-<path d="M0.04145 0.04432l6.56351 8.77603L0 15.95564h1.48651l5.78263-6.24705 4.6722 6.24705h5.05865l-6.9328-9.26967L16.21504.04432h-1.48651l-5.32552 5.75341L5.1001.04432H.04145Zm2.18602 1.09497h2.32396l10.26221 13.72122h-2.32396L2.22747 1.13928Z" fill="#A39FA9"/>
-</svg>

adev/src/assets/icons/browserconfig.xml

@@ -1,9 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<browserconfig>
-    <msapplication>
-        <tile>
-            <square150x150logo src="/assets/icons/mstile-150x150.png"/>
-            <TileColor>#e90464</TileColor>
-        </tile>
-    </msapplication>
-</browserconfig>

adev/src/index.html

@@ -64,8 +64,6 @@
 
     <meta name="apple-mobile-web-app-title" content="Angular" />
     <meta name="application-name" content="Angular" />
-    <meta name="msapplication-TileColor" content="#e90464" />
-    <meta name="msapplication-config" content="/assets/icons/browserconfig.xml" />
     <meta name="theme-color" content="#ffffff" />
 
     <!-- Open Graph / Facebook -->