dt-bindings: timer: Remove binding for energymicro,efm32-timer.txt

The driver has been removed by commit 523d83ef
("clocksource/drivers/efm32: Drop unused timer code") that's why binding
doc shouldn't be also valid anymore.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/571fc4b2e6d41c61b7f4445601a79bb50aace2e7.1628245879.git.michal.simek@xilinx.com


Signed-off-by: Rob Herring <robh@kernel.org>