Fixes #11741: Don't set headings font-family again, just use inherit

customize.html

@@ -436,7 +436,7 @@ base_url: "../"
     <div class="row">
       <div class="col-lg-6">
         <label>@headings-font-family</label>
-        <input type="text" class="form-control" placeholder="@font-family-base" data-var="@headings-font-family">
+        <input type="text" class="form-control" placeholder="inherit" data-var="@headings-font-family">
         <label>@headings-font-weight</label>
         <input type="text" class="form-control" placeholder="500" data-var="@headings-font-weight">
       </div>

dist/css/bootstrap.css

@@ -397,7 +397,7 @@ h6,
 .h4,
 .h5,
 .h6 {
-  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
+  font-family: inherit;
   font-weight: 500;
   line-height: 1.1;
   color: inherit;

less/variables.less

@@ -58,7 +58,7 @@
 @line-height-base:        1.428571429; // 20/14
 @line-height-computed:    floor(@font-size-base * @line-height-base); // ~20px
 
-@headings-font-family:    @font-family-base;
+@headings-font-family:    inherit;
 @headings-font-weight:    500;
 @headings-line-height:    1.1;
 @headings-color:          inherit;