ARM: dts: r8a7794: Remove nonexistent thermal sensor clock

According to the latest information, there is no thermal IP block
present on the r8a7794 SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>