ARM: dts: exynos: drop old thermal properties from Exynos4210

The samsung,tmu_gain and samsung,tmu_reference_voltage properties of
Exynos Thermal Management Unit driver are not used since April 2018.
They were removed with commit fccfe099 ("thermal: exynos: remove
parsing of samsung,tmu_gain property") and commit 61020d18
("thermal: exynos: remove parsing of samsung, tmu_reference_voltage
property"), so drop them also from Exynos4210 DTS.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220122132554.65192-1-krzysztof.kozlowski@canonical.com