update(docs): remove refs to

Fixes #7143.

src/components/chips/demoCustomSeparatorKeys/index.html

@@ -2,7 +2,6 @@
   <md-content class="md-padding" layout="column">
 
     <h2 class="md-title">Use <code>md-separator-keys</code> to customize the key codes which trigger chip creation.</h2>
-    <p>Common key codes found in <code>$mdConstant.KEY_CODE</code> can be used alongside your own.</p>
     <md-chips
       ng-model="ctrl.tags"
       md-separator-keys="ctrl.keys"

src/components/gridList/grid-list.js

@@ -38,7 +38,7 @@ angular.module('material.components.gridList', ['material.core'])
  *
  * The `md-grid-list` directive supports "responsive" attributes, which allow
  * different `md-cols`, `md-gutter` and `md-row-height` values depending on the
- * currently matching media query (as defined in `$mdConstant.MEDIA`).
+ * currently matching media query.
  *
  * In order to set a responsive attribute, first define the fallback value with
  * the standard attribute name, then add additional attributes with the
@@ -654,7 +654,7 @@ function GridLayoutFactory($mdUtil) {
  *
  * The `md-grid-tile` directive supports "responsive" attributes, which allow
  * different `md-rowspan` and `md-colspan` values depending on the currently
- * matching media query (as defined in `$mdConstant.MEDIA`).
+ * matching media query.
  *
  * In order to set a responsive attribute, first define the fallback value with
  * the standard attribute name, then add additional attributes with the