dt-bindings: clock: Drop st,stm32h7-rcc.txt

The binding is already covered by st,stm32-rcc.yaml.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20250505161933.1432791-1-robh@kernel.org
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Author: robherring