Remove vendor prefixed style properties

Author: dmitryrogozhny

src/controls/placeholder/PlaceholderComponent.module.scss

@@ -1,14 +1,9 @@
 @import '~office-ui-fabric-react/dist/sass/References.scss';
 
 .placeholder {
-    display: -webkit-box;
-    display: -ms-flexbox;
     display: flex;
 
     .placeholderContainer {
-        -webkit-box-align: center;
-        -ms-flex-align: center;
-        -ms-grid-row-align: center;
         align-items: center;
         color: "[theme:neutralSecondary, default: #666666]";
         background-color: "[theme:neutralLighter, default: #f4f4f4]";