include: gnss: dt-bindings: remove unused header file

This file contains macro definitions for baudrates that are not needed ;
probably leftover from an earlier iteration of the binding that used an
enum for the baudrate(?)

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

Author: kartben

MAINTAINERS.yml

@@ -1643,7 +1643,6 @@ Documentation Infrastructure:
     - include/zephyr/drivers/gnss/
     - include/zephyr/gnss/
     - dts/bindings/gnss/
-    - include/zephyr/dt-bindings/gnss/
     - tests/drivers/build_all/gnss/
     - tests/drivers/gnss/
     - tests/subsys/gnss/