ARM: dts: r8a7743: Remove legacy "renesas,rcar-thermal" compatibility

The thermal hardware description for the RZ/G1M SoC was added to its DTS
after the introduction of support for thermal zones, and included a
thermal-zones node from the beginning.

Hence there is no need to claim compatibility with
"renesas,rcar-thermal", which would be needed only for backwards
compatibility with kernels predating thermal zone support.

Fixes: 6c76b4f7 ("ARM: dts: r8a7743: Add thermal device to DT")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>