[docs] Fix IconButton Snackbar demos (#12964)

* Remove styles for IconButton

* Prettify the changes

* keep the height invariant

Author: bhalahariharan

docs/src/pages/demos/snackbars/ConsecutiveSnackbars.js

@@ -8,8 +8,7 @@ import CloseIcon from '@material-ui/icons/Close';
 
 const styles = theme => ({
   close: {
-    width: theme.spacing.unit * 4,
-    height: theme.spacing.unit * 4,
+    padding: theme.spacing.unit / 2,
   },
 });
 

docs/src/pages/demos/snackbars/SimpleSnackbar.js

@@ -8,8 +8,7 @@ import CloseIcon from '@material-ui/icons/Close';
 
 const styles = theme => ({
   close: {
-    width: theme.spacing.unit * 4,
-    height: theme.spacing.unit * 4,
+    padding: theme.spacing.unit / 2,
   },
 });