Update close vars

* Remove dupe hover color var (again, it's not necessary to have it's
own var here since we're controlling it via `opacity`)
* Add to customizer

customize.html

@@ -1191,9 +1191,16 @@ lead: Customize Bootstrap's components, LESS variables, and jQuery plugins to ge
           <p class="help-block">Popover outer arrow color</p>
         </div>
       </div>
+
+      <h2 id="variables-close">Close button</h2>
+      <label>@close-color</label>
+      <input type="text" placeholder="#000">
+      <label>@close-text-shadow</label>
+      <input type="text" placeholder="0 1px 0 #fff">
+
       <h2 id="variables-other">Other</h2>
       <div class="row">
-      <div class="col-lg-6">
+        <div class="col-lg-6">
           <label>@hr-border</label>
           <input type="text" placeholder="@gray-lighter">
           <p class="help-block">Horizontal line color</p>