Drop CSS icons for SVGs (#22708)

* add the svg icon as a partial so we can include it easily

* add the icon to the homepage

* drop .bd-booticon for svgs here

* rip out the import for .bd-booticon sass file

* Delete _booticon.scss

* indentation

* Update bootstrap-icon.html

* remove those

docs/assets/scss/_booticon.scss

@@ -1,25 +0,0 @@
-//
-// Bootstrap "B" Booticon
-//
-
-.bd-booticon {
-  display: block;
-  width: 9rem;
-  height: 9rem;
-  font-size: 6.5rem;
-  line-height: 9rem;
-  color: #fff;
-  text-align: center;
-  cursor: default;
-  background-color: $bd-purple;
-  border-radius: 15%;
-
-  &.inverse {
-    color: $bd-purple;
-    background-color: #fff;
-  }
-  &.outline {
-    background-color: transparent;
-    border: 1px solid $bd-purple-light;
-  }
-}

docs/assets/scss/docs.scss

@@ -39,7 +39,6 @@ $bd-warning:        #f0ad4e;
 $bd-info:           #5bc0de;
 
 // Load docs components
-@import "booticon";
 @import "nav";
 @import "masthead";
 @import "featurettes";