Drop Bower support (#23568)

bower.json

@@ -1,37 +1 @@
-{
-  "name": "bootstrap",
-  "description": "The most popular front-end framework for developing responsive, mobile first projects on the web.",
-  "keywords": [
-    "css",
-    "js",
-    "sass",
-    "mobile-first",
-    "responsive",
-    "front-end",
-    "framework",
-    "web"
-  ],
-  "homepage": "https://getbootstrap.com",
-  "license": "MIT",
-  "moduleType": "globals",
-  "main": [
-    "scss/bootstrap.scss",
-    "dist/js/bootstrap.js"
-  ],
-  "ignore": [
-    "/.*",
-    "/_*",
-    "about",
-    "assets",
-    "docs",
-    "js/tests",
-    "nuget",
-    "CNAME",
-    "composer.json",
-    "Gruntfile.js"
-  ],
-  "dependencies": {
-    "jquery": ">=3.0.0",
-    "popper.js": "^1.12.3"
-  }
-}
+@$% Not a Bower package. Use a better package management tool instead. ^&*