Revert "raise fullscreen windows on top of all other X11 windows"

This reverts commit 0659a0d98c.

It was a fix for dzen2 setups, but broke several other use cases.
Because dzen2 is not really important since most people use i3bar
nowadays, let’s revert this.

fixes #1062
fixes #1068
fixes #1070

include/x.h

@@ -93,12 +93,8 @@ void x_push_changes(Con *con);
  * Raises the specified container in the internal stack of X windows. The
  * next call to x_push_changes() will make the change visible in X11.
  *
- * If above_all is true, the X11 window will be raised to the top
- * of the stack. This should only be used for precisely one fullscreen
- * window per output.
- *
  */
-void x_raise_con(Con *con, bool above_all);
+void x_raise_con(Con *con);
 
 /**
  * Sets the WM_NAME property (so, no UTF8, but used only for debugging anyways)