dts: st: remove stm32mp13* from dts/st/mp1 folder

Since commit def7e1a0 ("dts: st: add pinctrl dtsi for STM32MP13 series")
all stm32mp13* related pinctrls are located within the
dts/st/mp13/ folder hence remove the old versions.

Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>