ARM: dts: stm32: remove some timer duplicate unit-address on stm32f7 series

Several unused "timer" are duplicate nodes of "timers" nodes.
There are two dt-schemas:
- timer/st,stm32-timer.yaml: A timer is needed on STM32F7 series, on all
  boards, to act as clockevent.
- mfd/st,stm32-timers.yaml: Timers can be used for other purpose.

By default, timer5 is left enabled to be used as clockevent. Remove all
other timer clockevent nodes that are currently unused and duplicated.

This removes several messages: Warning (unique_unit_address): /soc/timer@..
duplicate unit-address (also used in node /soc/timers@...)

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>