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

Documentation/devicetree/bindings/timer/energymicro,efm32-timer.txt

-* EFM32 timer hardware
-
-The efm32 Giant Gecko SoCs come with four 16 bit timers. Two counters can be
-connected to form a 32 bit counter. Each timer has three Compare/Capture
-channels and can be used as PWM or Quadrature Decoder. Available clock sources
-are the cpu's HFPERCLK (with a 10-bit prescaler) or an external pin.
-
-Required properties:
-- compatible : Should be "energymicro,efm32-timer"
-- reg : Address and length of the register set
-- clocks : Should contain a reference to the HFPERCLK
-
-Optional properties:
-- interrupts : Reference to the timer interrupt
-
-Example:
-
-timer@40010c00 {
-	compatible = "energymicro,efm32-timer";
-	reg = <0x40010c00 0x400>;
-	interrupts = <14>;
-	clocks = <&cmu clk_HFPERCLKTIMER3>;
-};