doc: cmake package: remove stale cmake version lines

This page is meant to document the behavior of the Zephyr cmake
package. However, its example CMake snippets contain some stale
references to a minimum version (3.13.1, now 3.20).

These lines are a bit of a distraction anyway, so just remove them.
They matter in general, but they don't matter where the Zephyr cmake
package is concerned.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
1 file changed