Refactor CSS for the bottom controls (seek bar & panel).

Change-Id: I908afa57b0db4ff462275c675fd257d7a78a2dc3

ui/less/containers.less

@@ -127,9 +127,8 @@
 /* Container for controls positioned at the bottom of the video container:
  * controls button panel and the seek bar. */
 .shaka-bottom-controls {
-  width: 98%;
+  width: 96%;
   padding: 0;
-  padding-left: 2%;
   padding-bottom: 2.5%;
 
   /* Position the bottom panel in front of other controls (play button and
@@ -145,7 +144,6 @@
  * in the middle. */
 .shaka-controls-button-panel {
   /* Fill the space horizontally, with no extra padding or margin. */
-  width: 98.5%;
   padding: 0;
   margin: 0;
 

ui/less/range_elements.less

@@ -176,11 +176,6 @@
   }
 }
 
-.shaka-seek-bar-container {
-  /* TODO: Document why! */
-  width: 96.5%;
-}
-
 .shaka-range-element {
   .range-element();
 }