Do not use deprecated MyGUI properties

Reported by @fr3dz10 on Discord. See e.g. the HP bar in the lower left corner:

Health bar references:

• XML skin MW_Track_Red: https://gitlab.com/OpenMW/openmw/-/blob/master/files/mygui/openmw_progress.skin.xml

  <Resource type="ResourceSkin" name="MW_Track_Red" size="2 14" texture="textures\menu_bar_gray.dds" >
    <Property key="Colour" value="#{fontcolour=health}"/>
    <BasisSkin type="MainSkin" offset="0 0 16 16" align="Stretch">
      <State name="normal" offset="0 0 16 16"/>
    </BasisSkin>
  </Resource>

• XML Layout (name="Health"): https://gitlab.com/OpenMW/openmw/-/blob/master/files/mygui/openmw_hud.layout:

  <Widget type="ProgressBar" skin="MW_EnergyBar_Red" position="0 0 65 12" align="Left Bottom" name="Health">
    <Property key="NeedMouse" value="false"/>
  </Widget>

Filed https://github.com/MyGUI/mygui/issues/214