task-x11*: remove in favor of packagegroup-core-x11* variants from oe-core

* packagegroup-core-x11* allows to remove task-x11-server and
  task-x11 from meta-oe without loosing any functionality
* be carefull with 2 changed default values:
  XSERVER does not include xf86-input-mouse and xf86-input-keyboard
  VIRTUAL-RUNTIME_xserver_common defaults to x11-common in oe-core
  and to xserver-common in meta-oe's task-x11

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>