Extract list-unstyled mixin; closes #17792

/fyi @mdo

scss/_mixins.scss

@@ -33,6 +33,7 @@
 @import "mixins/alert";
 @import "mixins/buttons";
 @import "mixins/pagination";
+@import "mixins/lists";
 @import "mixins/list-group";
 @import "mixins/nav-divider";
 @import "mixins/forms";

scss/_type.scss

@@ -85,17 +85,14 @@ mark,
 // Lists
 //
 
-// Unstyled keeps list items block level, just removes default browser padding and list-style
 .list-unstyled {
-  padding-left: 0;
-  list-style: none;
+  @include list-unstyled;
 }
 
 // Inline turns list items into inline-block
 .list-inline {
-  padding-left: 0;
+  @include list-unstyled;
   margin-left: -5px;
-  list-style: none;
 
   > li {
     display: inline-block;

scss/mixins/_lists.scss

@@ -0,0 +1,7 @@
+// Lists
+
+// Unstyled keeps list items block level, just removes default browser padding and list-style
+@mixin list-unstyled {
+  padding-left: 0;
+  list-style: none;
+}