arm64: dts: imx8mm-var-som-symphony: Remove unneeded i2c3 properties

The i2c3 clock frequency and pin configuration are already set by
imx8mm-var-som.dtsi.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>