fix(dialog): remove whitespace from "custom" dialog demo

  Remove extra unnecessary padding from right button that was probably left over by accident.

  Material Design specifies 8dp (6px) between the right edge of the right-most button and the right
  edge of the containing dialog.

  See https://www.google.com/design/spec/components/dialogs.html#dialogs-behavior

  This was added in b401751 for #3135.  It should probably have been removed in 3aab9e4.

Closes #8271

src/components/dialog/demoBasicUsage/dialog1.tmpl.html

@@ -36,7 +36,7 @@ <h2>Using .md-dialog-content class that sets the padding as the spec</h2>
  <md-button ng-click="answer('not useful')">
  Not Useful
  </md-button>
- <md-button ng-click="answer('useful')" style="margin-right:20px;">
+ <md-button ng-click="answer('useful')">
  Useful
  </md-button>
  </md-dialog-actions>