ARM: dts: stm32mp15: remove mmc alias

Remove the mmc alias no more required as the sequence number
of mmc device is used for boot_instance.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>

arch/arm/dts/stm32mp157a-dk1-u-boot.dtsi

@@ -10,7 +10,6 @@
 / {
 	aliases {
 		i2c3 = &i2c4;
-		mmc0 = &sdmmc1;
 		usb0 = &usbotg_hs;
 	};
 	config {

arch/arm/dts/stm32mp157c-ed1-u-boot.dtsi

@@ -10,8 +10,6 @@
 / {
 	aliases {
 		i2c3 = &i2c4;
-		mmc0 = &sdmmc1;
-		mmc1 = &sdmmc2;
 	};
 
 	config {