ARM: dts: stm32: remove useless clock-names from RTC node on stm32f746

On stm32f7 family RTC node doesn't need clock-names property.
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32f746.dtsi

@@ -300,7 +300,6 @@ rtc: rtc@40002800 {
 			compatible = "st,stm32-rtc";
 			reg = <0x40002800 0x400>;
 			clocks = <&rcc 1 CLK_RTC>;
-			clock-names = "ck_rtc";
 			assigned-clocks = <&rcc 1 CLK_RTC>;
 			assigned-clock-parents = <&rcc 1 CLK_LSE>;
 			interrupt-parent = <&exti>;