ARM: dts: STiH410-B2260: clean unnecessary hdmi node overlay

sti-hdmi is already enabled in stih410.dtsi.
So no need to declare it here.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>