remove unnecessary bg declarations in buttons per #5684

docs/assets/css/bootstrap.css

@@ -3180,10 +3180,6 @@ button.close {
 .btn:hover {
   color: #333333;
   text-decoration: none;
-  background-color: #e6e6e6;
-  *background-color: #d9d9d9;
-  /* Buttons in IE7 don't get borders, so darken on hover */
-
   background-position: 0 -15px;
   -webkit-transition: background-position 0.1s linear;
      -moz-transition: background-position 0.1s linear;
@@ -3199,8 +3195,6 @@ button.close {
 
 .btn.active,
 .btn:active {
-  background-color: #e6e6e6;
-  background-color: #d9d9d9 \9;
   background-image: none;
   outline: 0;
   -webkit-box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.15), 0 1px 2px rgba(0, 0, 0, 0.05);
@@ -3211,7 +3205,6 @@ button.close {
 .btn.disabled,
 .btn[disabled] {
   cursor: default;
-  background-color: #e6e6e6;
   background-image: none;
   opacity: 0.65;
   filter: alpha(opacity=65);

less/buttons.less

@@ -30,8 +30,6 @@
   &:hover {
     color: @grayDark;
     text-decoration: none;
-    background-color: darken(@white, 10%);
-    *background-color: darken(@white, 15%); /* Buttons in IE7 don't get borders, so darken on hover */
     background-position: 0 -15px;
 
     // transition is only when going to hover, otherwise the background
@@ -47,8 +45,6 @@
   // Active state
   &.active,
   &:active {
-    background-color: darken(@white, 10%);
-    background-color: darken(@white, 15%) e("\9");
     background-image: none;
     outline: 0;
     .box-shadow(~"inset 0 2px 4px rgba(0,0,0,.15), 0 1px 2px rgba(0,0,0,.05)");
@@ -58,7 +54,6 @@
   &.disabled,
   &[disabled] {
     cursor: default;
-    background-color: darken(@white, 10%);
     background-image: none;
     .opacity(65);
     .box-shadow(none);